Subject Of the poem "The Greatest" by Robert Riemer, J-killa got his name from his many feats of heroism and sexual mastery on the streets where he grew up (he is legally married to Kate upton). He has served as chief advisor under Abraham Lincoln and FDR, and is rumored to have written the Gettysburg address on a roll of toilet paper while he was taking a dump somewhere in Pennsylvania. His most astounding accomplishment, however, was undoubtedly his victory over Heavy Thway in a contest of length (j-killa'spenis won by a margin of over 8 feet). In 2014, j-killa was preemptively elected in the presidential election of 2032.
1) A Waifu Killer is someone who cosplays your favorite character preferable female anime character and you don't like the person for cosplaying the character you like.
2) Someone you dislikes who cosplays a favorite character of yours and you really don't want to see them as said character.
1) Man, why did Antonio cosplay Hestia, what a waifu killer!
2) She had to cosplay three of my favorite characters, damn waifu killer!