I suppose "oh, brother" has the same meaning as sighing. Then, can I say "oh, sister" as well?
"Oh, brother" is an informal exclamation used to express disappointment or frustration. "Oh, sister" is not used at all, but expressions like "oh, boy" and "oh, man" are! Ex: Oh, brother. Here we go again. Ex: Oh, boy. I accidentally messed it up again.
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