Someone who is an idiot, annoying person, jerk, etc.
The act of doing something stupid, lame or annoying.
Something that is rather lame, tedious, annoying, uncool, bad, etc.
Schmitty: That Shane guy is such a derf.
Joe: Yeah, he really derfed up that photo.
Cameron: It was such a derfy thing to do.
Brodie: Derfalicious indeed.