verb: To "ass out" is akin to "passing out," although it generally means going to sleep in a haphazard manner as opposed to becoming unconscious. For instance, after a long night of partying, one will generally ass out as soon as they get home, often falling asleep with their clothes still on or maybe on a couch.
"Hey Jim, is Steve passed out on your floor?"
"Nah, he's just sleeping. We were out really late, and he just assed out as soon as we got back."