Here's a great example of Justin's disheveled spiky haircut at 102.7 KIIS FM's Wango Tango 2012 Concert.
The sides of this one are shaved close to the scalp and the side burns come down to a point in front of the ears. The bangs are spiked up with mouse and the whole top is messed up for a less than perfect look, although he always seems to look perfect no matter what.