a homosexual male who disguises his sexulaity in order to get ahead
-"Look at our old mate behind the bar with his bumchum. This was a great pub, no look at it - cocktails, no real ale - and full of style-conscious genlemen with nice fingernails"
-"yeah, our old mate was always a stealth bummer. He'd come and join us with his frustrated wife and join us, but he was just casing the joint."
-"yeah, taken out by a stealth bummer!"
Someone who is obviously gay but hides it from the world for some reasons which are usually not so plain to see.
Greig's not gay (even though he's fucked everyone this side of manchester)