I haven't actually doe that myself - must have had a charmed life i guess - buyt know several instances of others doing it!
On a works night out, one of my female colleagues telling another female colleage about her mother-in-law who is French, and is apparently blessed with, and I quote "A huge witchy nose, a real de-Gaulle conk ..." at which point both our pairs of eyes became riiveted to the listener's hooter which would do an anteater proud! I was just SO glad it wasn;t me, but I blushed in sympathy anyway!
A couple of friends of mine have the spuse / offspring scenario on a regular basis. he is 53, and looks older, bald, what bit left is grey, she is 35, looks about 19, and they work together in a computer consultancy business. So when either of them meets the other's clients, there is always "I spoke with your father / daughter last week about this ..." which makes them laugh, but the clients are always dreadfully embarassed!