Is my girlfriend too sensitive?

ok so im talking to my girlfriend and out of nowhere she says like this catchphrase or something (i dunno one of her hero's from a band says it so she says it too.) and i simply tell her that she'll be saying that till she's on her deathbed. then all of a sudden she goes nuts and starts to ask me " oh thats nice so your thinking about me dying? thats the sweetest thing anyone has ever said to me besides " i hope you die". and it made me feel really guilty...really did i say something wrong? i think i just simply said that she'll be saying that till she dies because she likes to say it alot...its not like i said i wanted her to die or anything.