Most Helpful Guys
To see if the girl plays along or if the girl gets flustered. Just to see what kind of interest the girl has for the guy, because it can either be a crush or a sexual desire or the girl won't even care. Sometimes playing mind games is a good way to find out how the girl sees the guy
Its most probably to try and sex out of you. The only other thing is to get an ego boost trying to get your attention. If a guy is playing games with you, don't bother with him anymore move on.
Most Helpful Girl
Well, worst case scenario, is that he's a sociopath.
Or maybe he's simply trying to 'test' you. It's really hard to tell. You need to specify what kind of mind games he's playing.