I'm going out with this guy, and I joked around that it was a gym date, but I wasn't serious.
Why would you choose the gym for a date?
I thought it was the only place I could take him where he wouldn't be violent.
Don't do this if you're serious about him. Stringing him along like this is wrong.
It's not stringing him along if I'm just going to meet him there and leave immediately.
He might see it as stringing him along if you call it a date and leave immediately. If you're afraid he'll be violent if you don't meet at a public place like a gym, you're putting yourself in danger because you don't know what he'll do when you try to leave. You shouldn't meet him at all if you're going to leave right away.