An upside-down, dizzy goofball.
"That dude just tried to walk up the down escalator while singing "Surfin' Bird!" He's a real funky bat!"
A man who responds to friendly attention with an obsession that is largely disproportionate to the amount of given attention. This is characterized by cluelessness about a girl's feelings, a determination to "get the girl", and use of stalker-like techniques to try to win her over.
All I did I was 'hi' to him and he started being a funky bat. I had to block his number.