Fuck tee is a tee shirt worn by a male or female who is uncomfortable with their weight so they wear a shirt to hide the top half of their bodies when having sex.
When a person having sex leaves only their shirt on in an awkward way to not expose themselves due to being self conscious about their body.
joe: hey what did you do lastnight?
steve: went over that girls house.
joe: how did that go?
steve: not to bad except she wore a fuck tee when we had sex, said she didnt like showing her body