i'm not sure if i'd just walk out, or if i'd make a scene and get the staff to call the cops...indecent exposure is a form of assault.
the idea of the date is to find out if we want to be sexual or not. inflicting that on me without consent is illegal.
The dude's not a random off the street. I'd probably not want police involved. (I don't like police, anyway.) But I think if I somehow did manage to see what he was doing under the table, I'd tell him to put it away. I would let him know I was offended. If we could manage to reconnect after such stupidity, that would be cool. If not, I'm really good at getting out of touch.
I went out with this guy, years ago. I knew he was a little socially awkward from conversations we had before we met up. We had a lot in common, and he was good-looking, funny, talented, laid-back, just my type. We took turns choosing activities, and on one of his turns, he took me to some Korean karaoke bar. There was no dance floor, but we were tipsy and we danced anyway. At one point, his dancing was more like humping me, which was not welcome at all. He was basically rubbing his dick all over me in public. I also didn't like all the places he was putting his hands. I found it embarrassing.
So, I placed a hand on his chest to back him up, and shook my head no. I sat down, and when he joined me, I whispered my objections into his ear. He blushed, apologized, and did not do any of it again. By the end of the night, we'd rebuilt all the good will we'd had before the humping/groping incident, and I went to his apartment and fucked him.
I don't object to instant sex, nor to flirting, or direct propositions. Some things do cross the line for me, but a sincere apology and corrective actions can repair a lot of damage. Of course, that depends how good things were before they got broken.