I dont know how to respond to his jokes?

I have a teacher (from a hobby) and he has a family. He is a really cool guy (no douchebag, not arrogant, happy) but I sometimes wonder what he is thinking.
He jokes around with everyone (which makes him cool) and I know that whatever he says isn't serious, but I never know how to respond.

He says he can't read me. He jokes about marrying me, he tries to let me flirt with other guys and yesterday he asked me if I was going to change clothes and then he said: ‘Okay, ill wait and watch’. And he stopped his car and waited (even though he has a passenger).

Normally he laughs a bit, but he looked super serious in his wing mirror at me. And he kept waiting. Eventually I said it wasn't going to happen and I said goodbye. He drove off and then I switched clothes. I know he wasn't for real, but I found it really awkward. I never know how to respond to him. he's fun and I have no problem with him, but that joke was a bit weird bc he was so serious. He is used to people doing what he tells them when he fools around. What was he thinking? What should I do next time?
I dont know how to respond to his jokes?
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