It's unclear if Quinn actually knows Jem's name, but they use nicknames for everyone so maybe they don't know anyone's name? Or they just like nicknames. All of these things are equally possible.

Jem, meanwhile, is far too much of a pansexual dumpster fire to deal with so many pretty people calling him by nicknames. Like, the number's currently at two (Quinn and Curt) but that is two too many for his poor little brain.

If you listen really really closely, you can hear the gears clogging up and see the smoke drifting from his ears as his brain shuts off.

Also I adore the way Quinn looks in this outfit, may end up making it their every-day outfit, we'll see.