Amos, sometimes when we become irritated by someone else's behaviour, we are actually seeing things we despise about ourself only we see it magnified in someone else.
For instance, if deep down in side I feel kind of stupid (for no valid reason, I just do) then I may find myself being more judgemental or criticial about someone else's stupidity.
It is a lot easier to see the things we don't like in someone else than to honestly face seeing how we truly feel about ourself.

Little Neo