How about I  say I can't help but laugh at flat chested women?
You must be joking. Why do you laugh at them?
For physiological reasons.
Laughing at and judging someone based on their appearance is extremely rude and close-minded. You are hurting people by laughing at them for something they can't control. It's also wrong to objectify a woman which is what you're doing.
I'm just laughing at them and it's not like women with big boobs are perfect.
Looks are not everything, and people can't help how they look. You could make people feel bad about themselves and make yourself look rude. Do you really want this for everyone?