You and Swap papyrus are enemies, him and you always fight, he's never actually shown any anger or frustration and it pissses you off so you start trying to make him angry by saying rude stuff about him to him, he either shrugs, or responds with "eh" or "okay", Until you say something rude about his brother, Blue (swap sans)

the second you say it he snaps and yells at you

"OKAY MOTHERFUCKER NOW YOU GOT MY ATTENTION."