When a male surprises a woman expecting to recieve sexual intercourse through the vagina and unexpectedly recieves a surprise anally. Can be used as a verb or a noun. --BigDaddayWood
Noun: Anabelle, expecting intercourse through her vagina, recieved a Santa Sack Surprise from her boyfriend Carlos, who gave it to her anally.
Verb: Carlos Santa Sack Surprised his girlfriend Anabelle and Anabelle was flustered