Implies strong disapproval or dissatisfaction towards someone, often in an unfair manner. Whenever we lose a game, the coach dumps on us instead of encouraging us.
Pro Tip 2/3
Emotional Impact
Can make the person on the receiving end feel targeted and demoralized. It's not fair that you dump on me every time you're in a bad mood.
Pro Tip 3/3
Non-literal
It's a metaphorical use, meaning no physical dumping occurs. My sister always dumps on me for her own mistakes.