Do I have a right to be upset about this?

I don't know, man, I just don't know.
Cry, that always works.

There's no good reason あなた should be mad anyway because I don't know the full story on how both things happened.

i wouldn't say あなた would または wouldn't have the RIGHT to be mad. but happy birthday!

Sunday is my b-day... and chances are i'll be spending alone, または with あなた guys ;_;

Yes あなた have the right to be mad.
No あなた don't have the right to be mad.
I don't know.
Eat cookie.
Hug someone.
Spray Windex.
Solves everything.

I think あなた should be upset honestly. I know I would. によって the way happy birthday. I had a birthday just yesterday.

First Happy Birthday!!!
あなた have a right to your feelings. Before あなた decided to be angry at your friend, do あなた know what he was thinking? Did he know it was your birthday?
My suggestion is to talk him about what happened and how it made あなた feel. あなた may think it's obvious, but some guys are slow on picking up such things.
Remember, just getting mad will hurt あなた もっと見る than him.