Bf wanted me to pay more in tips

I went out with my bf to a bar and when he went to the bathroom some guy next to us was being obnoxious asking where I’m from and when I said “who knows where I’m from. Maybe I’m from here”. There were a few more exchanges and when we were done and the obnoxious guy left, two bartenders (one who was serving us and another that was there who was a bartender but did not serve us) both apologized for the absurdity and obnoxiousness. I said whatever it’s fine. I don’t care.

The bartender who was serving us gave me a to-go drink for free. My bf who came back from the bathroom noticed this and I told him that some guy was being weird and I’d explain later. I didn’t want to tell him the details while we were still at the bar since there were other customers within earshot and the bartenders that heard everything. When he noticed that I only left an 18% tip he got so mad because I got a free “to go” drink and that I didn’t include the price of the drink in the tip. He took the receipt and rewrote the amount of tip I put and put down more.

We later sat down somewhere else and I explained to him what happened but he still didn’t care. He said you should have tipped 20% and Included the to-go price of the drink in the tip , but when I explained how I was pretty much harassed and the bartenders gave me a drink out of pity he didn’t care. He still insisted I was being cheap for the 18% tip and it should’ve included the price of the drink on top of that. I apologized and said I didn’t know these bartender tipping rules but he didn’t care. The total of the tab was like 30$ but he crossed out my tip amount and included his own value. FYI this is on my credit card and I was paying for the entire tab. I ended up crying in public from what I thought would’ve been a romantic date.

Not sure if he was justified for treating me this way and if I was being “cheap” for my tip. How much would you all have tipped? I’m so frustrated