Can someone tell me what this means "pfft" I see it in tags on tumblr posts *good and bad* but I can't tell what it stands for. :/?

It doesn't stand for anything, it is just a sound people make when they are brushing something off, basically saying it is ridiculous or they don't care.
You want me to jump into a fire? Pfft!

Have you ever watched Mr. Bean? He does that a lot, "pfft!".