How can I deal with this?

Okay I am like so fed up with this. Okay I have a myspace account rite? And I like to go on my schools homepage sometimes and you know post into the topics from time to time. Well there's this little girl on there I ain't gone say her name but her and her sister is always goin on there startin $#!+ with me. I mean I say nothing to them never even said 2 words to them when we were at the same school she never said half the things she says on there to my face. She's always saying things like I'm a loser and I need to get a life but yet and still she's the one getting on and off the internet starting bullcrap. When I say things back to her her sister get's all up in it. Then she had the audacity to tell me that I was lying about being pregnant both of them. I don't like to lose my temper but I'm like 2 seconds from just cursing them out. Can someone tell me how to deal with these dummies?