stranger danger

1. The concept that any adult who is a stranger is potentially dangerous. Used especially when educating small children. When my son was old enough to play in our neighborhood on his own, we sat down and explained stranger danger to him so that he wouldn't go off with anyone he didn't know.

2. slang Used facetiously to indicate someone whom one does not know and finds perturbing or awkward as a result. A: "Who's that weird guy standing in the corner?" B: "Yikes, stranger danger!"