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Sexual relations with someone you consider as close as a family member, but who is not legally your relative. May feel awkwardly like regular incest, but is generally more socially accepted.
Person 1: So like... me and Mike have known each other for a while... but he's like a brother to me, if I bang him won't that be wrong?

Person 2: Naw, that's only psuedo-incest, go get yourself a piece o' his sausage.
by Fatality January 09, 2006
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