Overreacting to a somewhat overwhelming situation for the person twilighting, but for others, the situation isn’t that bad. The person tends to overthink, overplan, and hyperventilate.
Friend: Uh, hey, are you doing alright?
Twilighter: Hehe, yeah! I’m doing alright! Just need 7,432 things to do before the big event happens- OH WHO AM I KIDDING I AM NOT OKAY THERE IS SO MUCH TO DO BY TOMORROW!
Friend: Wow, you are twilighting hard.
It's a song, you sex-obsessed idiots! A perfectly innocent Owl City song about a guy who misses his girlfriend (or perhaps even a platonic friend, it isn't clear). Stop trying to turn it into something dirty.
When he uses the term, "Vanilla Twilight", he is literally talking about the color of the sky:
I'll find repose in new ways
Though I haven't slept in two days
'Cause cold nostalgia chills me to the bone
But drenched in vanillatwilight I'll sit on the front porch all night
Waist deep in thought because when
I think of you I don't feel so alone
Twilightlicious is a brony meme originating from a vocal tweet by Tara Strong, the voice actor for Twilight Sparkle (A character in the rather popular My Little Pony: Friendship is Magic universe)
The format is a small rhyme, usually centered around the basic elements of the character (Twilight being the exception, as the fandom typically portrays her as more of a troll)
"I'm the T to the W-I, L-I-G-H-T, and ain't no other ponytroll it down like me: I'm Twilightlicious"
Twilight Sparkle