If I choose to use the expression "In my humble opinion" then I am being polite. I am leaving others a way to avoid taking offence, of thinking that I am not being too dogmatic. If others ascribe my opinions as being humble they are passing a judgement that is rude. They are not disagreeing with my expressed opinion but they are saying that my opinion is a humble one, not worthy of consideration, beneath their own "lofty" opinion .... I thought I should explain that since it is so clearly misunderstood. So carry on taking the piss chaps. It is your own ignorance that you are demonstrating.
It is that same as those among you who insist that they are Mr Soandso. Mr is a title awarded by others out of respect for you. It is not and should never be a title you assume for yourself. I never announce myself as Mr. When asked for my name I give it. Nothing more and nothing less. When asked for my opinion I give it, nothing more and nothing less.
Learn to live with it.