I always say “What was that…?” or “Say what…?”
I’m trying to stop though because I think it’s kinda rude. I think it would be better for me to say the more dignified “Sorry, what did you say?” Seems more polite. But habits are hard to break!!
Easier said than done, buddy.
Seriously though, I say “Sorry?” Happens a lot on the phone, I don’t know why.
A couple of years ago, all the kids were saying “Wha’ happened?” I think that’s pretty much over now. Good thing, because it was stupid.
The title of the thread is the answer to the question. Now that I think about it, though, if I’m incredulous about what the person said – as opposed to having trouble understanding the words themselves – I’ll append a “now” to the phrase. Thus:
“Do what?” 
“Do what now?” :dubious:
I just say -
pardon?
Me too. If I’m not wretchedly tired. If I am, it’s “WHAT??”
To my patients: “I’m sorry, I didn’t quite catch that, would you mind saying it again, please?”
To my friends-" Sorry, I missed that, what were you saying?"
To my husband-“Say it again Sam!”
It’s a “bit” we do because I space out so often.
People who say "Beg yours’.
I think this is an ‘Australianism’.
You did what to who’s cat?
(must give credit for that to my co-worker, had never heard it until I met her)
The informal is, “do what?”
The formal is, “pardon me (or excuse me), I didn’t catch that.”
To my secretary, it’s “what was that again? I CAN’T HEAR YOU!!!” Bellowed, because for some reason we both refuse to use the intercom on our desks and prefer instead simply to yell at each other. I am told that my coworkers love that about us. 
8a) Howzat?
8a.1) Howzat again?
8b) Run that by me again? (usually pron. “Runnatbymegin?”)
Oh yeah…Cincinnatians say, “Please?”
- Excuse me? If I think they’re being jerks
- Say that ** again? when I truly didn’t hear them**
- I’m sorry? I use this the most.
Sorry? or Excuse me?
Occasionally, if I’m annoyed, it’s…Could you please repeat yourself, you were mumbling
I can’t abide “huh?” and cringe to hear myself ever saying it.
“I’m sorry, what was that?” (Or either half of this)
“Could you repeat that, please?”
Sometimes I won’t say anything, just indicate by expression and gesturing at my ear.
If I know damn well what you said and I’m not happy about it, it’s “What did you just say?”
If I’m not understanding when people talk I usually point out that I’m a bit hard-of-hearing. This usually helps vastly.
If I’m with the family, “¿Mandeloqué?” which would be something like the country-bumpkin, run-together version of “sorry, what did you say?”
With English-speaking friends, “mindsa’in’atagain?”
And in polite company, either “sorry, I didn’t understand that, could you repeat please?” or its Spanish equivalent. If they were talking too fast I’ll specify “… repeat more slowly…”
I’ve been told I can “pass” as American so long as I’m not overtired. I didn’t quite believe it until that run-in with a server at my company’s cafeteria, who wouldn’t believe I didn’t know what “Okrah” was and needed her to point it for me. Sometimes I do understand the sounds, I just have no idea what they mean.
Do what? At work.
Shot who? At home.
Que? Everywhere else.
“Your what hurts?” or simply “What?” with friends
“I’m sorry?” or “Could you repeat that?” when at work.