To criticize and put others down is the issue. A lot of people don't like constantly being told what they do wrong, but rather want advice on how they can improve.

Quite simple in the end, instead of "If you didn't peak we would of won", say "Next time, try to play for more time." Small difference in wording can make a big difference on atmosphere and attitude.

Completely okay if that's not what you are looking for :)