First off, you won't be laughing because he falls off - you'll be laughing because he'll be curled up in a fetal position from the pain. That'll be the end of him telling you that girls have it tougher because of boobs.
As for the bouncing boobies comments -- tell him he'll never learn how to ride horses if all he thinks about is riding women. Now is that too crass for this this forum? I don't know, but your bf sounds like a piece. Tell him to get over himself and the whole man thing already.
Seriously now, for your own benefit, it would probably be a really good idea to invest in a good sport bra. I am small busted, so don't have the bouncing problem, but I know many women that do and they have all kinds of solutions. Before really good sports bras came out, I knew a girl that would wear her bra, then a t-shirt, then have a friend wrap her boobs down with duct tape so she could play baseball.
OH, and when your bf is in that fetal position, just laugh. Don't offer up any solutions. He doesn't deserve any.