A person of large structure that not only participates in twat like behavior but is basically a twat all the time. They tend to have sister wife hair and have shoes a small child could sleep in.
Oh look there's that gargantutwat. I expect she is off to tell someone how to do something she has never done before.
Person 1: Did you see that video of the guy whose nuts were so big, he couldn't even go outside?
Person 2: I know! He had gargantuan balls.
Person 1: I hope he gets better.