With All Due Respect...

From the Macmillan English Dictionary Blog:

A double-edged sword

Posted by Sharon Creese on December 22, 2010 

Using set phrases can be a good way for a student to sound more natural and fluent in English, but they can also be something of a double-edged sword.

Consider with all due respect – at first glance, it suggests that you are trying to be respectful, whilst expressing a different opinion, but native speakers know that it can also be used to say the exact opposite. You may be genuinely using it to say:

I respect you as a person, but I’m about to disagree with you

which is fine, but you could also be saying:

I’m pretending to be respectful because you are in a position of authority and I have to, but actually I think you’re a fool. As long as I keep pretending, though, you can’t do anything about it.

The difficulty, of course, lies in the fact that the other person has no way of knowing what you really meant; they might assume it’s the latter, when really it wasn’t. Students could find themselves unexpectedly in the doghouse, simply because they tried to be a bit ambitious in their language choice.

Source: http://www.macmillandictionaryblog.com/a-double-edged-sword