Smelly Opponent
This is actually good strategy on his part. Next time he should let off a couple farts--silently of course--to amplify the effects to their maximum potential. I don't really play OTB anymore, but if I ever do again I'll definitely be giving this a try.
You could"ve just played your move and start walking around the tournament hall until he made his move and then go back to your board lol
That makes it worse because you get a little used to the fish smell if you stay there. But if you keep getting up then you're reintroduced to the fish smell each time
Please complain next time, and be sure to videotape the arbiter laughing in your face and telling you to grow up.
In my OTB game earlier my opponent was some 55 year old homeless looking guy who smelled like fish ...
But I was wondering if I can call an arbiter if my opponent smells a lot? ...
https://handbook.fide.com/chapter/e012023
"12.2.3 ensure that a good playing environment is maintained,
12.2.4 ensure that the players are not disturbed,"
If it's an fide tourney, yes.

In my OTB game earlier my opponent was some 55 year old homeless looking guy who smelled like fish so I wanted the game to be over with as quickly as possible. I was playing the whole time with my shirt covering my mouth and nose.
I played this really dumb tactic that didn't even work but he misplayed it and I won. I was out of there within 2 hours which is pretty quick.
But I was wondering if I can call an arbiter if my opponent smells a lot? It was really distracting and I could've easily lost just because I wanted to leave asap. Even in round 1 when I wasn't playing him I could smell him.