Oh, anonymous friend, thanks for the request of an elaboration~
Keep in mind, Lucifer is one of the characters I probably have the least amount of cards for, minus the dateable non-dateables. That's a real shame in hindsight.
In general, he's kinda old-fashioned, so when he says words like hullabaloo, it catches me off guard. I die laughing every time. Like how Mammon has a habit of saying words like sassafras. I love it.
He is also easily riled up when his brothers or MC make a jab at Lucifer being romantically involved with Diavolo, going so far to tell Satan "Fuck you, Satan" on one occasion. Lucifer rarely cusses compared to most of his brothers, and this is the one and only time we see the word fuck being used. So, that definitely shows how frazzled Satan got him.
On Lucifer cussing, because it's seldom to when he's really mad or serious, it takes me off guard and gets a few good giggles out of me, like when he says "Damn, and it's making up for lost time" in Braids and Purple Flowers and "What the hell is this?!" in Quality Time for Two and, what I assume he does, summons his brothers into the dining room with magic first thing in the morning.
Lucifer isn't a classical dumbass like his brothers. He's more of urbane and unintentional dumbass that when something goes over his head, something he doesn't catch with a double entendre, it makes it even funnier.
For example, this moment from Seven Rulers of Hell (Lucifer) Devilgram:
Like, seriously?? Even Simeon caught what MC was hinting at by commenting "Ignorance is a bliss."
There's another example of Lucifer being either totally unaware or pulling off being ignorant by disguising his desire to complain to MC about Diavolo's unintentional slight against him being unable to cook a specific type of cookies in Lucifer's Melancholy:
No, not when you're intentionally doing something that basically indicates that you want to talk about something that is obviously bothering you. I absolutely want to believe that he does this unintentionally, because it makes it equivalently funnier if he's doing it on purpose.
The man's pride has been tested by Diavolo's comment, and the idiot who avatars over pride doesn't even know why he feels so offended by it.
By the end of the Devilgram, Lucifer and MC are covered in flour, and Lucifer has failed spectacularly at making cigar cookies so badly "they could kill a man." The whole ordeal is worthless after everything, because Lucifer just flips Diavolo's words around to make himself feel better in the most prideful way and devaluing Barbatos.
Lucifer likes to believe he's more mature and composed compared to his younger brothers, but he can be just as immature, especially when he teases Satan about being his father in technical terms rather than his brother. Lucifer can also have a bratty attitude when he tests Satan's patience with certain comments or when he gets competitive with him like in Lesson 9.
The audio drama Don't Read Over My Shoulder is another good example of Lucifer being an irritating shit to Satan by disturbing him while he's trying to read and spoilering the ending of the book.
In another audio drama, Show Your True Self, Lucifer is giving Satan unsolicited help with a heartfelt message, and at one point Lucifer just, I think, hugs the stuffed toy and makes some... suggestive noises. Like, peak unintentional groans that sound dirty. I lost my shit and cringed a little, honestly.
He can be a dumbass in soft ways when he takes care of his brothers in genuine caring fashion like in Being The Oldest. Whenever anyone mentions this side of his character, he gets defensive and brushes off the comments, but he can't seriously believe that his excuses work. He's tsundere-like with his brothers, and it's funny in a cute way.
Not to mention other tidbits of moments of Lucifer reducing his better-than-thou mindset during certain events like when No. 2 asks who wants to be MC's partner in the wedding event or when he, along with Mammon and Levi, shouts "Gross!" in Let Your Hair Down.
Oh my God, I almost forgot the moment in 8-19! The first pillow fight of the game, and Lucifer makes comments such as "Anyone who dares throw a pillow at Diavolo must DIE!" and "All right, any of you brave enough to take a pillow to the face, step forward" and proceeds to catch pillows on fire and make a hole in a bed, not to mention knock out his brothers with pillows. Peak idiocy. He was going to scold his brothers for the exact same thing, but Lucifer takes it up to another level and causes more damage.
He can complain about being dragged into troublesome events because of his brothers, but he can get just as caught up into the moment and drop his mature attitude
In the audio drama Save Me, Lucifer, Lucifer gets fed up with his brothers calling his name, so he eventually bans them from saying it for a month. It's such a goofy restriction, though, because banning them from saying his name doesn't stop them from still pestering him. He's just tired of hearing his name being cried over and over again, so he makes his name off limits. Like, that's just silly! Poor Dia, also, because Lucifer snaps at him before realizing who said his name. Poor guy needs a proper break from the House of Lamentation, Diavolo, and all his responsibilities.
Lucifer can and has ultimately blamed MC out of frustration for either (harmless) ideas that Diavolo gets from them or if something happens to interfere with his plans.
Speaking of being childish! Let me mention the The Joy of Doing Nothing Devilgram:
Honestly, any moment involving Simeon embarrassing the hell out of Lucifer is gold, because it immediately reduces Lucy to a mess.
Lucifer also knows about kabudon, and that's as hilarious as it is shocking for him to know about, even more funny because it's only brought up during a strategy meeting in a dating game trying to woo MC.
Mentioning games reminds me of Devil Kart: Game On!
If anyone has played a racing game as a kid or simply gotten invested into the race, you remember leaning as the car rounded turns like you're actually in the car. To know Lucifer does this is simply astoundingly funny.
Of course, let us not forget, in the anime when Lucifer is by himself playing the app game and Satan walks in on him sticking his tongue out.
Or when Mammon finally gets his body back from being magically dognapped, Lucifer, along with the others, is devastated at the loss of Good Boy Mammon. The fact Lucifer plays along with this situation instead of fixing it is too much for me
The man can't enjoy being goofy in peace, but he also can't hold that persona he puts on 100% of the time. Those small fractures and moments of literal dumbassery or character breaks make Lucifer so much more appealing as a character, and I lose my shit every time.
Lucifer isn't just a stuck-up, prideful, arrogant, abusive, controlling, self-centered basic bitch for Diavolo. He's got his sweet moments, his down moments, his cute moments, his relatable moments, and importantly, his when-am-I-not-serious not serious moments where he easily jokes or teases MC.
I'm sure there are more moments from the Lessons and Devilgrams that I don't have, so feel free to add your favorite moments or thoughts too.
