When I was in high school a friend called me a pussy about 8x a day. I got sick of it, so I started responding "you are what you eat." And after a few days he said that my comeback was getting old. I explained how I only do the comeback to the insult, so if the comeback is getting old, so is the insult.
The reason I share this story is because the only way he is going to change is through him wanting to. I suggest you do something similar - if every time he complains about bad dps, say the same canned response. Make it repetitive so he starts to get sick of it and wants to change on his own.