Definitions
1.nounFecal matter produced by bats
2.nounNonsense, horseshit; especially when said by or attributed to someone irrational.
3.nounExtreme irrationality or unreasonableness, insanity, craziness.
4.adjectiveExtremely irrational or unreasonable, insane, crazy."Don't take any courses from that professor. She's completely batshit."
5.adverbUsed as an intensifier, particularly for insane or synonyms."When we heard about it he went batshit nuts."