Noun/adjective. Flagrantly, obstinately stupid, in a way that shows you have no idea that your own best interests, or even your survival, are at stake. The word was apparantly coined by Nicholas Gurewitch in the Perry Bible Fellowship comic strip (date unknown, post 2002--it appears in comic #62 on the PBF web site). When used in derogatory response to someone else's idea or statement, weeaboo can serve as a euphemism for 'bullshit.' Can also serve as a euphemism for 'clusterfuck' to describe a bunch of people acting stupid in some inconvenient way.
Stuffing yourself with hot dogs and sauerkraut right before going into the ring for a boxing match is weeaboo.
That guy at the mike is totally spitting some weeaboo.
There was some kind of weeaboo on the highway this morning and traffic was all backed up.