Really crazy, in a loopy, delusional sense. May derive from the sense of 'as crazy as someone who believes in aliens' i.e. to the extent of wearing tinfoil hats, or, less likely, someone who thinks as differently from a normal person as someone from another planet would.
"Why is Donna pacing in circles mumbling to herself?" "I dunno, the girl is as crazy as aliens."
by stellar760 October 08, 2013