-Bring your GI Joes with you and play war with the fish.
-Spear Fish
-Treasure Hunt
-Collect things
-Sneak into a marina and surface next to people and tell them you are lost, or make up some story about a sea monster or something, see how gullible they are.
-scuba into the swim area and sneak up on cute girls.
-make a fake shark fin and scare everyone in the swim area
-Go Deeper, or shallower, going places gives you something to do.
-I like to dive different spots every time I go out, the best thing you can do is wreck or cave dive, you never get bored, if you are always checking out a new wreck or a new cave.
-photography
-grow an underwater garden
-make an underwater fort.
-make your own mini-wreck.
-Make an underwater preserve of your own.
-set up underwater scare crows in places where people dive a lot.
-go diving with someone new.
-I can go on and on and on. There is a lot of stuff to do underwater, I got bored before too, if you can't tell.