I don't think this is actually much of a big deal, but I can tune a guitar by ear no matter how out of tune.

My uncle is a guitar afficionado, and we got into an argument when I said I could. He said you needed some kind of reference note or something like that. Wouldn't give up. So I grabbed a guitar, scrambled all the tuning and tuned it.

He bowed in awe, but I think he just never realized he's not as musically inclined as he'd like to be? Maybe it's not common, but I highly doubt it's impressively rare.....