英文回答:1. Come on.2. Cut it out.3. Give me a break. 中文回答：这事儿不归你管，你管也没用，别白费力气了

Forget it!

It means "Cut it out!"

don't waste time keep it don't do things in vein

it's mean don't do anything even if you do it very well , it just waste your time , or something else.