I've not had any issues like these when out by myself, but it reminds me of a couple group incidents.
1) I'm a member of
Photowalking Utah and there was a group of about 12-16 of us walking around downtown. We stopped at this interesting hotel entrance that had some limited space. So most of us were standing around with our cameras, bags and tripods while we took turns in in twos and threes shooting this doorway. A car drove past slowly, did a U-turn, came back the other way, did another U-turn and stopped. The question asked was "Who are you waiting for?" They thought we were a bunch of paparazzi waiting for someone famous to come out the door. The didn't quite get it when we told them we were taking pictures of the door itself.
2) One of the founders of the Photowalking Utah group, my friend
Rich Legg, was out shooting on location in downtown SLC with a
Kenneth Linge seminar, again with a bunch of photographers standing around with gear, when someone stopped and asked him "Is this the Photowalking Utah group I've heard about?" Sort of ironic that, of all the people to ask, they'd pick him.