It's often (over)used by floggers and teenagers, it can be used in replace of 'whatever', 'lol', 'wtf', 'omg', etc.
You can also use 'ahre' before a sentence to express disagreement and tell what do you think is da truth.
Boy1: Hey dude can I have some cookies?
Boy2: I don't have any cookies dude.
Boy1: Ahre! I just saw a bag of cookies in your desk!