Yikes OP, I know how painful it is just to have a strap snapped back, I don't even want to imagine it snapping and breaking. At least they didn't know the noise came from you though, that just would've added to the the awkwardness/embarrassment. A few years ago when my family and I were trying out mattresses in a furniture store, my bra broke and I had to sorta hold it in place while still having a conversation with the salesman about which mattress I found the most comfortable. It wasn't an enjoyable experience to say the least.

You should've clutched your chest like you were shot, then looked down & said "they missed"

I agree. Mine has snapped before and I never felt much, aside from the mild irritation of having to fix it.

Either your bra was an old bra, you were wearing it too tight or it was a size too small. You should have at least felt discomfort from your bra strap being too tight around you to make you want to loosen it. If you couldn't loosen it, you should've worn a different bra or have gone bra shopping beforehand if you knew your bras weren't fitting properly anymore. Things may be tough at the moment but you still need to look after your boobies!

One of your brother's friends has skills.

This couldn't be more of a non issue. I've had it happen before and it's irritating but barely painful. Saying that you had to hold back tears of pain is a bit much. There's nothing wrong with saying that your bra broke so you'll need to go to the nearest bathroom to fix it.

Oh snap!

At least yours can snap. :/

Reminds me when the rubber bands used to pop in my mouth when I had braces

That must have been a Bust!