Imo, if it's a normal game, don't be that person. Especially if you're playing someone who isn't seen often. Instead, if your opponent is struggling, help them. They might be new to the champ they're playing, or new to playing against the champ your playing.
I had a game a LONG time ago, back when I used a wireless mouse, where my mouse died. I had said it in all chat when they questioned where I was. My opponent, who was the mid laner, could've used that time to push hard. Instead, she froze the lane and allowed me to try and catch up when I was able to actually join in all so the game wouldn't be her stomping me and an actual match.
We ended up talking to each other through out the game, giving each other tips on the others champ and build. As for the game? It was fun, back and forth. I don't remember who won, but I do remember that I enjoyed myself, which wouldn't have happened if my enemy was an ass.