Send it to me from the girl you like, and I advise you to be kind. What do you mean?

"I advise you to be kind" is used to satirize or persuade people with bad intentions, and it is also a kind of spit language.

First, it may be a joke. I am used to saying this sentence.

Second, I hope you are serious.

Third, I may have found something bad about you or influenced her.