I know exactly what you mean man.
I was training alongside this level 126+12 (138) guy last night and I kept thinking his name looked familiar and that I had seen him before.. Well almost a full hour went by and we were staying out of each other's way and keeping to ourselves, then right towards the end of a fight with a revenant, when I was almost completely out of supplies, he runs up to me and claw specs me out because I am at half health! Then I remembered that he was the same guy who had pulled some similar shit on me a few nights before at revs.
I didn't lose much, but I was super pissed at him. I guess he ran out of supplies too and just thought, "hey, I am heading to the bank anyways so I might as well spec out this kid". Fucking bastard!