I quite agree that being offended by what others say about oneself or one's general category, belief system, ethnicity, etc. admits one's own unresolved and tenuous self-esteem issues. What other people say about oneself, likewise, admits their own issues.
Obviously - what someone else thinks -- another's OPINION -- really has nothing significant to say about or to do with oneself, but merely expresses where that person is coming from, including a lifetime of input, experiences and individual ABILITY to respond to the person's outside world. Many folks walking around really are ill-at-ease with their own relationship to the world beyond themselves, so find fault or nit-picking reactions to others. If one happens to be in their sphere, one may be the target for such stuff, but it is invalid for one's own being & function.
We need to learn to give each other benefit of the doubt and keep our own self-image intact by living up to our own selves and potentials, not by trying to adjust to, suit or fit someone else's idea of what / who we 'should be'. I like the quaint advice that says, "Don't let anyone should on you!" :-)
Good question, kallini -! Hugs