Originating from ancient China, the word "Tabe" describes the act of using one's own chopsticks in sexual activities. "masu" Represents the anus of a male. Thus the meaning of the word all together is to shove chopstick(s) up a man's rectum.
"Hey man whats that thing called where you stick chopsticks up a dudes ass?"
"Oh, you mean Tabemasu? I did that with your dad last night!"