A friend alerted me to this article by Jessica Caldwell in The Times:

"The line to the bar was long, so when I arrived I ordered two Jack and Diets for myself. The best investment you’ll ever make is a large tip on your first drink.

I made my way downstairs. My favorite kind of dance floor is so dark and crowded that no one notices that I can’t dance, and this was that. I swayed to the beat without spilling either drink (talent) and scanned the crowd."

(...)

'The next two hours were a blur. So let’s call him Rick. He worked at an app. Everyone worked at an app. Liquor before beer or beer before liquor? I couldn’t remember which one was supposed to come first so I just went back and forth.

We were smoking again, out on the patio. My self-confidence was directly proportionate to my blood-alcohol level. I was Kate Moss. I pulled a bar stool between us. “Let’s arm wrestle,” I said. A command, not a question.

“Uhh, I don’t know. I bench 220. I was a high school quarterback …” he backpedaled.

“Stop making excuses,” I said.

We knelt down on the cement and put up our arms on the small uneven surface of the bar stool. He won the first round. We went left the second round.

“You’re letting me win,” I said. He just laughed. “Come on, arm wrestle me for real. Don’t be a girl!”

We went right again. My arm snapped in half. Rick had broken my humerus in two, a clean fracture. I bent my arm 90 degrees and watched my arm leave my arm. I took my left hand and held the two pieces of my right arm together. “Oh my God,” he said. He was freaking out. “Go close my tab and get us a cab. We’re going to the E.R.,” I said. Cool as a cucumber.'

Read the article here.

So, you can break the humerus of your love object on a first date with impunity, but you should take her to the E.R. And some people would argue that it's more charming not to break anybody's humerus.

This could be the line: "Let's arm wrestle, I promise you, I won't break your humerus."