An adjective used to describe a male who endeavours to spend as much time as possible being 'good friends' with other peoples girlfriends behind the back of the girls boyfriend. He will occasionally try to get too close with her and she may become aware of his true intentions, but this is only in lucky scenarios. Until then she will insist to her boyfriend that they are 'just good friends', which is frustrating for guys who know his true intentions which are obvious to males.
Similar to a 'schweff' but prefers girls who are taken for some sick reason.
1) Pete is getting too close with Philippa, mate, but she doesn't have a clue.
Similar to Slimy in the sense that it is used to describe a male who tries to become 'good friends' with other people's girlfriends, however in a Sludgy case, the girls themselves realise that he has more slimy intentions, whereas slimy guys manage to avoid the detection of their victims.
boy1) Pete is so slimy man...
boy2) nah hes actually so slimy he's sludgy - even she can tell.