A "likeout" is when you give a thumbs up to everything on someone's Facebook profile by using the the "Like" function. The likeout victim receives numerous notifications. The word is derived from "psychout" due to the fact that the victim does not know if their friend genuinely likes everything on the profile or not. (Usually they don't.)
Oh my God! Brandon, why did you likeout my profile?!
(The past tense of "likeout" is "likedout".)