The Hells Angels are going to war with MTV ... and one of the network's biggest stars ... who allegedly STOLE the motorcycle club's famous death head logo and plastered it on t-shirts. 

The man at the center of the controversy is "Fantasy Factory" star Rob Dyrdek ... whose company owns the "Young & Reckless" clothing label ... created by his cousin Chris "Drama" Pfaff.

The Hells Angels are suing Rob's company and MTV -- claiming Y&R designed and sold a bunch of t-shirts that "bear a design confusingly similar to the [flaming skull logo]" ... and they never asked for permission.

In the suit, filed in federal court in California, HA claims the logo has great commercial value ... because of its "very widespread public recognition" which evokes "strong and immediate reactions whenever used."

The Angels claim Dyrdek's actions have caused "substantial damage" to the biker club ... and believe MTV violated their rights by broadcasting the stolen logos on "Fantasy Factory."

The Angels are seeking unspecified damages. Calls to MTV and Rob Dyrdek have not been returned.

"Fantasy Factory" star Rob Dyrdek is $50,000 closer to building a dream skate park for kids in L.A. ... thanks to a HUGE donation from one of his co-stars.

Dyrdek has been super-passionate about building skate parks where kids can SAFELY skate whenever they want -- and now his former assistant Chris Pfaff (better known as Drama) is taking another cue from his mentor and helping the cause ... with a $50,000 donation.

In fact, Drama is so serious about the cause, he's also donating a portion of the profits from a new shirt and a new hoodie that his skate clothing company will be selling.


 
TMZ spoke to a rep for Drama ... who tells us, "[Pfaff] worked as Rob Dyrdek's assistant for multiple years picking up a lot of the skills and knowledge that Rob had for his businesses.  Now it's Drama's turn to give back to Rob's foundation by opening his very own safe spot skate spot."

Drama will present the check at a charity event for the Rob Dyrdek Foundation in L.A. this weekend. The exact location of the park has yet to be determined.

"Fantasy Factory" star Scott "Big Cat" Pfaff hasn't been to the dentist in 10 years -- and this week, he's gonna pay for it big time ... with multiple painful procedures.

Pfaff finally ended his decade-long dental sabbatical a few days ago -- and we're told the mouth doc immediately spotted multiple cavities ... and several teeth that need to be pulled.

Sources close to Big Cat tell us, he also has to get a root canal asap -- and the first of several pain-filled visits is scheduled for this week.

Don't forget to floss.

Rob Dyrdek's Fantasy Factory is in the middle of a major face-lift -- and it's all to make room for Big Black's new penis enhancement ... offices.

Sources close to the MTV production tell us Rob's co-star has inked a spokesman deal with Extenze male enhancement pills. We're told Big Black's new gig will require extra office space at the FF... so construction is underway and should be done before the new season premieres.

Wood for wood.