Why grown ups act like kids sometimes

There have recently been some startling incidents involving adults acting immature. Let me list a few notable ones:
1. Serena Williams lost a semifinal match at the US open because she threatened to "shove this f**king ball down the (linesperson's) throat" after she was called for a foot fault on her serve.

2. A congressman yelled liar during the president's speech to the congress regarding healthcare which was televised across the US.

3. Kanye West interrupted Taylor Swift's acceptance speech at the MMVAs and embarassed her by claiming that Beyonce's video was the best of all time.

Now these three cases all involved relatively famous people but immature behaviour in adults happens all the time. Have you ever seen what happens inside parliament especially in Asia? Do your parents ever drive through a yellow light? A red light? How do you think they would do in a road test that we have to take now based on their regular driving patterns.

It seems our society's notion of "grown up" refers more to the physical than to the personality and values. Afterall, humans like to make quick judgments about people and how difficult would it be if you had to judge someone's behaviour before determining if they were "grown up". Sure, parents will say "do as I say and not as I do" or "your generation will be better". Well, how many generations have we gone through now? I don't see much improving going on. Maybe I'm a cynic but the only plausible resolution (in my lifetime) to this problem would be to lower your expectations for "grown up" behaviour. Afterall, we are only human.