(v.) Something is either a). very good, or b). very bad. Depending on your sexual orientation, I suppose, although straight people can use it either way. Heavily dependent on context.
"We have a physics test today."
"Dude, that stuffs the butt."
"Have you seen the Linux XGL demo on Google Video?"
"Yeah - that video really stuffs the butt!"
"Landon, you really know how to stuff the butt."