How do I get my boyfriend to knock off this annoying habit?

Let me start by saying that I know this is a bit unusual for a post in this sub. I'm not looking for any supernatural help or paranormal assistance. I just need some advice on what to say to my boyfriend. The reason I'm asking here is because this is just so weird and I think you guys would have a fresh perspective on this issue.<br><br>My boyfriend and I have been together for three years. We have had an awesome time together overall, but one thing that he does is really annoying. He always, always, always knocks on the glass walls when we pass by aquariums. He'll tap his fingers on the glass, he'll rap upon it with his knuckles, or even smack it with the flat of his hand. He does this at aquariums, upon seeing fish tanks in restaurants, even the small aquariums at pet stores. I've mentioned to him how annoying it is but he doesn't seem to care.<br><br>In fact, he seems to find my irritation entertaining. He's made jokes about scaring the fish and how he's testing their durability. Whenever I drop it, he will bring it up again, like he's trying to start an argument.<br><br>This is the only thing he does that I find seriously annoying but it's SO annoying. What should I do or say to convince him to stop?