Seeing as how it seems multiplayer is now broken (for now), and I couldn't find one, here's a thread to post if you have all the achievements for BL1.
After almost 200 hours played, mostly playing casually with my friends, and a bit of fiddling to get a lan going to get the arena achievement I missed doing till yesterday, I finally went back and finished my last achievements.
♥♥♥♥ Moxxi's arenas, so much. They're not difficult, just tedious. I went through 5 movies getting through the 2 arenas I needed. At least with the claptrap drop achievements, you can just afk through it.