Those examples aren't really someone being brutally honest, it's just being rude.

Being brutally honest, is telling you best friend that that dress they love,just doesn't suit them.

Or the expensive new hair cut they got is....awful.
Is telling your tone deaf sister to just stop going on x factor because she cannot hit a note.

Telling the woman who just came out of the toilets her skirt is caught in her knickers.

Brutally honest, is not the same as being plain rude.

Sorry you have encountered these idiots though.
All the best.