People who have loud, obnoxious cell phone ring tones...and let everyone within 500 feet of them hear it.
Hey now, nothing wrong with that... better than the same ringtone everyone has so that 20 people look at their phone to see if its them.

I have one of those anoying ringtones... but its incubus so its badass.
what drives me nuts is people that will sit and wait for a close spot in the parking lot when you're not even in you're car yet... just getting to it to unlock it... Then i proceed to sit in it until they leave, and as soon as they leave then I back out.
Rule of thumb, if the revers lights aren't on, don't stop and wait... Lazy biotches...