To wank over a woman (or man)
The spiller is a man who masturbating over a woman or another man
1. One who, at a party or other reasonable facsimiles of social gatherings "spills" their shots, mixed drinks, beers, cocktails, and any other alcohol-laden beverages down a sink, into a toilet, out a window, etc. whilst pretending that they are more inebriated than they truly are; i.e., pretending that they have actually consumed the amount of alcohol that all their empty beer cans/shot glasses/red plastic cups would suggest.
2. Any such person who pretends that they are more drunk than they really are, even if they do not physically commit the act of spilling.
"Chris cannot hold liquor for his asshole's sake but he's a well known "spiller" so he was mostly just putting on a drunk act. He wants to say he's had as much as everyone else but he knows he'd be floored if he did, so he's always sneaking over to the window or making fifty trips to the john and then he comes back asking for another drink."
-The Basketball Diaries