I’m bound to say/I have to say: used when you are going to say something that may annoy or upset someone, especially because it expresses criticism:
I’m bound to say/I have to say, I found his performance pretty disappointing.
With respect/With all due respect: used when you are going to disagree with someone or criticize someone, in order to sound more polite:
With all due respect, Mr Davies, I do think you’re being a little unreasonable.
To say the least/To put it mildly: used for suggesting that something is worse or more extreme than you are saying:
I think his behaviour in the meeting was immature, to put it mildly.
I found the flight rather uncomfortable, to say the least.
Shall we say? used in the middle of a sentence for making a statement or criticism seem less severe or offensive:
The training programme seems, shall we say, a little dull.
Don’t get me wrong: used when you want to make sure that someone understands your comments correctly, especially when you are criticizing them:
Don’t get me wrong, I do like Christine, I just don’t think she’s right for you.
How shall I put it?/Let me put it this way: used when you are going to say something that is honest but may sound rude or unkind:
Her boyfriend is a bit, how shall I put it, difficult to get along with.
Let me put it this way, I wouldn’t miss her if she left.
Without wishing to do something: used when you are going to say something that someone may not like:
Without wishing to hurt your feelings, I think you need to lose a little weight.
To be fair/In all fairness/To give someone their due: used for making your criticism of someone or something seem less strong by mentioning something good about them:
Vicki’s schoolwork has been poor this term, though, to be fair, her maths has improved.
She never calls me, though to give her her due, she always remembers my birthday.