/annoyed (as per usual)
Ok, so, my friend wants me to pick him and his gf up. I don't mind if you give me gas money or food or something like that. I also tolerate when you want me to do it on a regular basis. What pisses me off is when you can't even give me a rough estimation of time of when you need me, therefore preventing me from doing anything. That just seems inconsiderate imo. What will make me rage is if I finally get a call back saying, "Oh, nah, we decided to see each other some other time." Sadly, that's what I'm expecting.
A reevaluation of the friendship is in order.
If he/she doesn't respect you enough as a friend to keep your needs in mind, then you are under no obligation to maintain the friendship.