In the mission Borderlands 2: Claptrap's Secret Stash, Claptrap wants you kill Ug-Thak, Lord of Skags. Ug-Thak is a powerful Skag boss.
Where to find Ug-Thak, Lord of Skags
Claptrap is just fooling around. You don't have to kill any Ug-Thak, Lord of Skags. Just find the stash in the conatainer across from Claptrap.