K-Daddy got Britney to pay his legal bills, claiming relative poverty. But, as her lawyer calls it, "Bank of Britney" may have been taken for a ride -- specifically, from L.A. to Vegas.

According to legal docs, in a recent eight-month period, Federleezy blew $50,489.71 on hotel rooms and refreshments in Vegas.

In one day alone, K-Fed dropped $2,632.50 at TAO Beach (the pool club at The Venetian). And on one wild evening, he spent $2,862.60 at TAO nightclub. One day at the Hard Rock Beach Club -- $3,008.33

Oh yeah, and there's this.... at Scores strip club, he once spent $365, but left a $2,000 tip.

And for this he dinged Brit? Dang.