This is probably the hardest achievement in the DLC to do solo since he is level 64 on both playthroughs. Crawmerax is a giant lobster type monster that you fight during the quest "You. Will. Die." The hardest part about him is that both he and the little minions he has running around him can take almost all your health in just one hit. This means that you need to use a lot of teamwork with your partners to ensure that no one is concentrated on by the enemy. The way to actually injure Crawmerax is to shoot the purple soft spots on his body. He has six in total - one in his eye, one on each of his four claws and one on his back. Once the final purple spot is destroyed, Crawmerax will fall and drop a LOT of loot (very rarely pearlescents though).
In addition to the above, there are a couple of other little tips that may help you defeat this giant lobster.
- For his minions that annoy the heck out of you, the Green Craw Worms are weak against fire, the Armored Craw Worms are weak against corrosive, and Craw Maggots are weak against shock.
- There is a spot you can get Crawmerax stuck in that can really help you kill him fast. Read HERE for more info. Thanks to Powerman1469 for the help.