Can be either used to insult someone or just a (friendly) greeting.
Guy II: Hey, what's up wallfucker?
Guy I: Ah, not much.
joe: gosh. you're a wall fucker.
look at that pile of fuck, he's such a wall fucker.
a couple who are dry humping/ making out in the middle of the club.
dancing against the back corner wall at The Loft in Itaewon, South Korea because to dance anywhere else would get you raped.