umm stiss 

when you stroke your penis up and down it makes an umm - stiss sound

he was beating his penis in the bathroom and you could hear an umm stiss sound from the next room

umm stiss by Anonymous March 30, 2003

umm stiss 

What's this?

"Fred drunkenly pulled down the transsexual's skirt, mumbling, 'umm stiss?'"

umm stiss by Professor Plum July 8, 2003