This is something that people would say if they feel that they are being annoyed by a female. There are times when people use this when they are just annoyed, and there are also some who use this when they feel that the female is a slut.
After saying, “Begone Thot!” People would usually try to shove, punch, slap, or move away from the “thot” or the annoying female. This is a phrase that is often used to do memes. For some people, using this phrase means that they are just discouraging slutty girls from trying to come on to them. They would like the slutty girls to go away.