Embarrassment....

Whilst I can't say that small children have never heard me describe something in profane terms... these have been rare exceptions and not the rule. Though there have certainly been many times I've thought in those terms outside of my home, unlike someone with Tourettes (for example) I am sufficiently aware of what is not appropriate and not indulged myself by publically broadcasting my opinion.

Embarrassment is something people fear, and something we all (to some extent) avoid.

When I've encountered it it's generally belonged to others and is, I suspect, often associated with those occasions when I have difficulty getting someone to repeat their comment(s).

Though this does make it more interesting  - 

-  for me.