I do when taking Liebs to places where his behaviour is likely to be innappropriate and other adults may be affected. I rarely do this as it isn't appropriate, but as you say sometimes you have no choice. Liebs has been to Uni lectures with me, class and tutor approved beforehand.

Comments in the supermarket are met with smiles and thanks: people either don't mean to be rude or intend to hurt, so I turn their comment to them. Really annoys the rude people. But I don't give details to randoms, just as I don't expect details when I talk to a child out and about.