Britney Spears is ready to open a can of whoopass on British actress Keira Knightley after the ‘Pirates of the Caribbean’ star blasted the rumored dead-beat mom over her penchant for going ‘commando.’

Keira said earlier this week: “I’m not going to get blind drunk and then stumble out and fall over and puke up in front of people. Celebs like her prove they’re sluttier than everybody else ’cause they don’t wear knickers.”

During Brit’s Friday night LAX Las Vegas hosting gig, the blonde responded with: “Who’s Keira Knightley?” “I guess she must needed the publicity,” adding, “I’m not going to get blind drunk and then stumble out and fall over and puke up in front of people. I’m not saying I don’t do that on my own in private, but I try not to.”