A: Someone hit Mark below the belt. And Mark is very upset these days.
B: That must have something to do with his girlfriend.
A: You are right. It is the one who was trying to beat Mark’s time.
B: It is vicious of him to do that.
hit sb. below the belt
Hit sb. below the belt的原意是“击打拳击手腰部以下的部位”，引申为“使用卑劣的手段，背后使坏”的意思。
e.g. I think if someone wants to criticize me, they should focus on my work. Mentioning my past alcohol problems is below the belt. Now everyone will change their opinion of me, and I don't deserve that.
e.g. The question for me is whether the public will go more against Mr. e.g. Davies for his marital failures or against Mr. Kraft for bringing them up. While Mr. Kraft's tactic was effective, it was also clearly below the belt.
have something to do with：与……有关，与……有牵连
e.g. Her diligence must have something to do with his success.
e.g. Does his visit have something to do with the meeting tomorrow?
beat someone’s time：向某人好的方面进攻，抢夺某人好的东西
e.g. Tom accused his brother of trying to beat his time.
表示某人做某事很毒辣，可以用这个句型“It is vicious of sb. to do something.”