If something makes your day, it has given your some pleasure or has made you happy. And sometimes the expression is used as a humorous way to show that the person you are speaking to knows it would be a big mistake to make your day. make my day常在口语中出现，表示什么事情让你特别高兴，有时候也是对特别不走运的事情的一种自嘲的说法。

Examples:
This joke is too funny. You make my day. 这笑话很有趣。让我很开心！
You want to fight? Go ahead, make my day. 你想打架？来吧。让我开心开心。