To do something incredibly stupid, repeatedly. Usually involves an action that is more harmful to yourself than others. Esp when involves lying.
I tried to help him out after his girlfriend kicked him out, but he thomas-upped and I had to bail him out of jail.
She was all over him, but he thomas'd it up and went home alone!
I invited him over for a drink, but he thomas'd me and I had to call the cops.
To get absurdly drunk, find the sloppiest chick in a party, then fuck her on the lawn of any structure (usually fraternity houses).
"Dude, Mike got way to messed up and ended up lawn sloshing last night."