Top definition
Any extraterrestrial, most likely with some level of insanity and/or psychotic tendencies, that poses as the sister of any legitimate human. May emit, at any volume, the following: doggy voice, shrill sounds, nonsensical words, sudden shouts, low hissing sounds, extremely bad whistling, or other bizarre noises.
"Why is my little sister so annoying?" "She's probably an alien psycho sister."
by Cameo March 31, 2005
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