Explosive allegations from douchebag hanger-on Sam Lufti were made public on Thursday when his trial against Britney Spears and her family began in Los Angeles.

Lufti says he acted as Britney's manager for eight months in 2007 and is thus entitled to 15 percent of her earnings from that time period -- the same time period during which she was in an emotional free-fall that her family says he helped cause.

He's also suing Britney's mom Lynne for defamation since she alleged in her book 'Through the Storm' that he drugged the singer and cut her off from her family. In addition, he's suing Brit's dad Jamie for supposedly punching him in the chest back in 2008.

Lufti's lawyer Joe Schleimer alleges that despite her family's claims, Britney's amphetamine use is what caused her breakdown -- not Lufti himself.

"Most of the things that went wrong related to that habit," said Schleimer, also noting that Britney suffered from paranoid delusions at the time. "My client sometimes spent 24 hours a day to prevent Britney from using drugs."

Lufti claims that he met Spears in a club and agreed to be her manager, but only if she gave up the drugs because "I don't want to be your manager when you overdose." (He's a sensitive guy, that one.)

And the supposed "real" reason she shaved her head? Spears allegedly told Lufti that she'd heard hair tests could reveal drug use, and she didn't want to risk testing positive and losing custody of her two young sons -- so she simply got rid of the evidence.

He also says that after convincing her to allow drug-sniffing dogs into her home, the animals found a baggie of white powder -- he claims Spears admitted it was crystal meth -- and drug residue in the carpets, which Lufti tore up and threw away.

Lufti blamed Spears' 2008 hospitalization on a 36-hour pill bender and says the day after she was admitted, dad Jamie punched him. Which is nicer than he deserved.

Many of Lufti's claims are refuted by a 2010 TMZ video in which he never mentions anything about Britney's drug use, saying instead that her head-shaving stunt was "a cool thing ... somebody expressing their artistic side ... I think she was just expressing her independence and her freedom ... there's nothing wrong with Britney. She's awesome."

But apparently not as awesome as her bank account.