Arin, who ties with Suzy for most controversial Grump. His constant negativity and bad gameplaying along with his opinions on the Sonic, Mario and Zelda franchise annoy some, while others love his irreverence and wit.
He's also very prone to fake stupidity and intentionally playing badly for laughs or to blame the game. This episode is particularly awful, with Dan suggesting Arin to throw a knife multiple times but Arin doesn't listen. He keeps making the same mistake of throwing the chainsaw, saying "duuuh" and screaming "I DON'T HAVE A KNIFE!" and unsurprisingly, he died. From the comment section itself you can see that some people think what he did was great because afterall, "Game Grumps is about fun, not about gameplay!" while others think it was annoying and posting a video with little to no progress in the game is, at best, disrespectful to the viewers.
Tv Tropes on why Arin is controversial. There's more on the YMMV page, but this was the main stuff. He also says Skyward Sword is worse than Sonic 06 and refuses to let anyone say anything positive about him. I quit the game out of boredom too, but there's enough for people to like