Short for "Master Tool", typically used to describe someone who sucks up to and does random shit for others. Also connotative of someone who is acting effeminate and showing a girl his "sensitive side" just to get some pooty.
Usually screamed repeatedly in a high-pitched voice (pronounced "Masta Teeeee!") by a group of people witnessing another person acting like a huge tool. The screams are oftentimes accompanied by the same gesture that referees use to call for a "time out".