This is the action of liking something on facebook and then immediately unliking it so that the person gets a notification that you liked their post, but when they check, they realize that you haven't
A "like psyche" is when you "like" something on Facebook, giving it a thumbs up, and then immediately "unlike" it. The person will receive a notification that you "like" their post, only to find the thumbs up is gone. This prank is most effective if accompanied by a comment about the sweet "like psyche" you just pulled.