I have come across several grown men called
Jonty, and they were all super-annoying twits. I think it's built into the name. Maybe it's the resemblance to Jaunty; it's like a big cheesy fake grin.
I like
Kit and
Jem and
Betty though, and don't think they're weird or snobby, though YCMV. I know several Jems, but I think they're all short for
Jeremy.