This is when you go to a hotel with a coworker for sex during the work day. It is called this because, much like a grilled cheese sandwich it is fun, tasty, and kinda sticky, but ultimately unhealthy.

Internet persona(s) who happens to follow you and you happen to follow them back and maintain communication with and have a mutual liking for eachother whether it be friendship wise, etc. (Mutuals if more than one mutual)