Accidentally giving someone anal. When you are not in any way intending to have sex with them but anal intercourse occurs.
"Yo man, how was that gig you went to last night?"
"Kind of weird. Someone spiked my drink with viagra, and then I was crushed up against this person in front of me, and accidentanal occurred."
"That is weird. What did they do?"
"He said he didn't mind. I think he was gay."
"It was a guy? Oh, shit man."