pile-on       
noun [ C ] uk/ˈpaɪlˌɒn/ us/ˈpaɪlˌɑːn/
 (对某人)群起攻之,发出猛烈的抨击
an argument or attack by a large group of people against one person or a much smaller group
  After his temper tantrum, a pile-on by commentators immediately ensued. 他发完脾气之后,马上就被各种评论人士群起而攻之。 
 The actor began a pile-on over some random tweet.  这名演员随机挑了一些推特大肆抨击。 
 - More examples
- It's disheartening to read of the inevitable pile-on that follows after somebody hits it big.
- She joined the pile-on, with a patronizing put down of the candidate as an ambitious dumb middle-class mom.
- Social media call-outs can quickly become a pile-on.