For me it's "that dude." You know, the guy in his late 40s/early 50s that lives in his mom's basement and rarely interacts with other human beings.
He comes to the show alone (obviously). Drinks too much and tries to dance his way into groups of women, who scatter like rabbits.
Later, he starts playing wildly aggressive air guitar in the middle of the dance floor, clearing the floor within about 12 seconds.
Later, he comes practically onto the stage to shout advice to the band in the middle of a song. ("DUDE! DUUUUDE! SLAP STYLE! SLAAAAAP STYYYYYYLE!!!!")
At break time, he won't leave you alone because he desperately wants to keep telling you how "effing awesome" you are...but that you'd be even "MORE effing awesome" if you just did more slap/more fills/turned up/thrashed more/etc.
Yeah, that guy. For some reason I see him too often.
That dude was at my gig about a month ago. He was also the "I was in a band once..." dude too. Some of the "Please help me!" looks on the women's faces were priceless.