If we're into embarrassing moments in shops her (rather than joining the Lew Dawson appreciation society with mother-in-law stories), I'll mention the time, back in my teaching days, when I was shopping with our Head of Drama in the ladies department of a large department store for costumes for a school play.
The play was Sir Gawain and the Green Knight, requiring mediaeval costumes with plenty of coloured tights. I was quietly browsing away when my colleague shouted at me from the other side of the department, holding up a pair of green tights as he did so. "Chris", he enquired at full volume, "do you think that these will fit a 14-year-old boy?".
We got some VERY odd looks from all the women who were shopping alongside us ;-)