He was there with David Reale (aka Glen Coco) or "Canadian Dave" from Skins US. Justin was incredibly nice, and had a great sense of humour too. He said to my friends and I "once we get inside, we can do a whole photo shoot." Unfortunately my friends camera was acting up. So while I struggled to take a picture, he was whispering to her "fire your camera man". He also told her "you're so tiny, I just want to pick you up".
With another friend of mine, he grabbed her camera and then took a selfie, and said "okay, that will be $5 for a selfie." He was very down to earth and funny! I didn't get a picture with him then, as David said they had to go. At that time, I was busy trying to figure out something other than Skins US that I recognized David from so I could ask for a picture with him as well.
Later when walking with my friend to the bar to get water, we ran into him again. He waved me over, and asked me what I wanted. I said a picture, and he said sure! I introduced myself and he said "Adam, I'm Justin". Trying not to be the ultimate bother, I thanked him, and we ran off to enjoy the rest of the concert after that! I later experienced a random 6 foot tall man attempting to jump on my shoulders, and I was not upset when he fell off.