If you were in, say,
Osaka, you'd be more likely to hear things like this (standard Tokyo dialect equivalents are in parethesis):
"sora chau de!" (Sore chigau yo!)
That's wrong/different!
"Chau chau!" (Chigau!)
No, no!
"Honma de?" (Hontou ni?)
Really?
"Wakaran!" or "Wakarahen." (Wakaranai)
I don't know / I don't get it / I don't understand.
"Sou yan ke?" or "Sou ya?" (Sou na no?) Is that so?
Slang and casual speech varies considerably from region to region in Japan and elsewhere. Personal experience suggests that learing the regional speech mannerisms will only make you more friends.
Kansai dialect is cool.