Gypnak is a term sometimes used to descibe someone with a gypsy background, a traveller or someone with a stong Irish accent. Alternatively it can be used to describe a particularly horrendous human being.
Oi! you manky gypnak tosser, i was saving that stale-ass bread for the birds. Fuck off!
S: That new guy is always brown-nosing the boss.
D: I know, he's a right Gypnak.