Obviously totally depends on the situation. If it's a hot chick, I'll just trip and fall on top of her.
I know when I trip or fall I don't try to play it off; I try to take as many people with me as possible.
Never laugh at a stranger, always help the person get up, regardless of age or sex. I guess I am a swoly on this thread and being a wet blanket. Unless it is someone that I am friends with, then I don't help, and ridicule endlessly.
Show concern first. Laugh later. I don't think falls and trips are funny. No problem being a wet blanket like that. Though since SOME people REALLY do fish for other's sympathy and might all "clutzy" for sympathy-baiting. That stuff is lame, thats when its appropriate to laugh AT them
Never laugh, draws unwarranted attention to yourself. Stand and stare to feign concern; based on age, gender and physical proximity relative to other bystanders, assist or move on.
Situational. I usually laugh at myself if I somehow escape without injury. One time I slipped and fell on some steep wooden stairs. I landed on my ass on the top step and bounced every step all the way down about 20 steps. I also had a cold so by the time I hit the bottom my face was covered in snot and I looked like I was the star of a gay bukkake scene. I stood up and laughed out of relief and the humor of it all. I could have died but just ended up with a sore ass and a face full of goo.
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Depends how fat the person falling is, I can't help but laugh if some big fat ass goes tumbling to the floor. Not saying I wouldn't help him up and ask if he's ok though...