First slice of cake always belongs to the person having the birthday. It's like you stole their wish after blowing out the candles. Next time try being patient and wait for the second slice at least.

She is just fat

In all fairness you tsking the first slice of someone elses cake is a dick move, but tbh convincing your gf you cheated on her is a dickmove on your sisters part.

You're an idiot and rude for taking the first piece of cake and obviously you're both too immature to be in a relationship

Everyone keeps saying you are immature for taking the first piece of cake. Yes, maybe you are. Maybe you do this sort of thing all the time and your sister was sick of it. Maybe you are a dick who doesn't think of other people. In this case, it doesn't warrant your sister murdering your relationship over cake. I kind of feel like this is a situation where your girlfriend got pretty lucky. I wouldn't want to have a potential SIL who destroys my happiness over cake.

....Megan!

Ross? Is that you?

Tell your sister thank you... This is a warning and your sister exposed the type of person this girlfriend really is.

dude if your bitchfriend is that stupid I think you know what to do (dumb the bitch) you dumass MOFO

I feel for your sister! I was sick on my birthday and never had any of my cake because my siblings ate it all. YDI