I have found throughout my aviation career that many people who significantly change personality when they get on the flight deck are actually under confident and/or lacking in ability themselves, and this often gets channeled into odd/aggressive behaviour. They are fine with a pint in their hands at the bar, because they are not in a high-pressure environment making critical decisions; this goes for people in training positions as well, who are good at telling others how to do it but aren’t that good at it themselves, and they know it.