"Kevin has always been hot-headed and he likes to bang things around," notes an insider. "Britney learnt to deal with him kicking the walls now and then.

"But lately, that sort of behavior has escalated to frightening new levels - and recently it hit crisis point."

Pals say things have been strangely calm between the warring couple lately - because they are never in the same city together. Brit, 24, and Kev, 28, have been leading separate lives since Jayden's birth in mid-September, with Britney staying home to raise her sons while Kevin crisscrosses the US to promote his debut rap CD.

Sources say Kevin Federline became angry after Britney made a crack about his recent appearance on the wrestling show WWE, where the crowd booed him as he made his way to the ring.

"Britney's laughing set Kevin off and he went wild," a pal reveals. "It was like he had weeks of pent up hostility in him, and all it took was one little comment to light the powder keg.

"He started screaming at her, smashing things and hitting the walls. Britney's seen him crazy, but she's never seen him like this and she's never been so fearful for her physical safety." While the couple's marital woes are an ongoing source of tension, insiders say Kev is irate that his rap career is tanking while buzz about Britney's pop comeback continues to build.

"He's gotten violent [before] and it's getting worse with each temper tantrum," notes a concerned pal. "He hasn't hit Britney or the kids, but after seeing the rage he's carrying around it could happen next."

In other news, Kevin Federline says promoting his new CD has put him "a couple of hundred grand in debt." But K-Fed's cry didn't sit well with Egypt and Ashy, who interviewed him on their Power 105.1 show reports PageSix. "You didn't struggle," Ashy taunted the rapper. "You got like 10 carats in your ear right now, son."