If a friend asks if you can treat him, it means that you treat him to like a chocolate bar and he is able to decide if he wants to treat you or not.
Joe: Hey bob, can you treat me to a Slurpee?
Bob: Yeah Sure!
2 weeks later
Bob: Hey Joe can you treat me this time?
Joe: Nah maybe some other time.
I personally will never be treating some of my friends again if they wont treat me back.