Losing a competition.

Getting fired from the job

Somebody having more wealth/beauty/popularity than you despite you yourself have it all just lesser.

Someone stealing your Girl

Probably should’ve been more specific, so my fault, but I was actually asking to name an example of a pure evil who has the pettiest Freudian excuse.

One of the transformers PEs has the excuse of losing a beatboxing competition.

Wanting to be loved by others

Sentinel Prime view doing good acts for others and having compassion as pathetic, which is the reason why he betrayed the primes.

Ashfur might not be PE, but he can very much qualify, so I'm putting his reason:

Your love rejecting you for someone else.