adj. Mentally wacky. Cuckoo for crack!
Related terms: batshit loony, batshit whacko, batshit insane, batshit nutty, batshit nutso, super-batshit-insane, completely-fucking-batshit-insane, batshit-fucking-crazy, batshit-sounding, non-batshit, pre-batshit, anti-batshit, batshit loonball, holy batshit, batshittery, batcrap, batpoop.
Real citation: “She has four bags filling the self-checkout area, blocking both bagging lanes, neglecting the intended use of the pull-out trays provided. Her empty cart is blocking my exit from the line. I begin bagging my stuff in the tiny space behind the ATM machine while the person behind me's purchases begin to bottleneck onto the scanner. The woman freaks out and begins stammering "so...that's your bag?" I nod, resisting the impulse to tell her no, I'm helping bag your crap because you're obviously batshit-demented and I don't want to be here all night.”
(Paul, “Night of the Living Deadheads - A Trip To Rainbow Grocery,” Feb. 8, 2005, http://www.limahuli.net/blog/archives/complaining/)
Made-up citation: "Who's crazier: a batshit-demented dude or a shithouse mouse? Further research is needed!"