Parents and girlfriend's entire family get mad at guy for taking birthday cake away from their spoiled 2-year-old who is sticking his hands in the cake: ‘Everyone glared at me like I was the most evil [person] on earth’

There will be times in life where everyone in the room seemingly agrees that you're in the wrong, while this might often mean that you are actually in the wrong and should apologize, that's not always actually the case. There can be any number of factors at play, including groupthink, favoritism, and social manipulation. All perpetrated by enablers and sycophants. This often happens with "rainbow" babies and other family favorites and golden children who can do no wrong and inexplicably get away with almost anything that none of their peers can. 

Unfortunately, it doesn't end with childhood and will continue throughout your life in your work and friend groups. Just because "groupthink" comes into play and a group agrees on something, doesn't mean it's the reality. The reality is, though, that if you're in a room with a bunch of people who are gaslighting you into thinking you're wrong when you have a moral and ethical reason behind your actions, you probably don't want to be in that room any longer.

Families are strange, especially so when they're not your own, and when this boyfriend attended his girlfriend's mom's birthday party, he was shocked by the behavior he witnessed from his girlfriend's nephew that no one was doing anything about. He gently intervened but earned the ire of the family in the process. While you can't blame someone for their family, if they don't see the problem, perhaps it's time to reconsider the relationship.