If the customer behind you accidental bumps you with their buggy, do you say something or just ignore it?

I turn around to see who it is.  If it's an elderly person, I don't usually say anything.  If it happens more than once, I might stand at the side of my cart or say something of it's someone younger who is leaning on their cart reading a magazine.  Take a look at folks these days - when did shopping carts become walkers?

i would just ignore it unless i got hurt bad

Funny you should ask!  Just yesterday I was in a grocery store standing between two displays.  I wasn't concerned about blocking a passageway because there were only a few other customers in the store.  Well, one came along and instead of politely asking me to move, pushed her cart into my back!  I said out loud to my wife that the lady had pushed me and stared at the woman in disbelief.  She (the woman)  just ignored me.

I turn around and shove the cart back at them, hard. (Only in my imagination, I really just ignore it).

If it's a hotty, I turn around and say thank you. Otherwise I ignore. Most people are polite and say "sorry". I say "no prob".

I bust a cap in their behind.  

"I just follow them home and that night .... !"

I ignore it until we get to the parking lot. Then I just run over them with my car.(Yes, I'm kidding)