Former
Guns 'N Roses drummer
Steven Adler just blew the lid off the rock star penis debate -- telling TMZ,
Steven Tyler from
Aerosmith has the biggest knee knocker he has ever seen ... period.

Adler dropped the big news on his tour bus in L.A. -- telling us, "After seeing Steven Tyler's rig ... I'm lucky if I take my clothes off at all after that."
Guess it's true what they say about guys with big mouths ...
Ex-
Guns N' Roses drummer
Steven Adler was in the mood for even more self-improvement after a successful stint in "
Celebrity Rehab" -- stopping by an L.A. tat shop on Tuesday to retouch some old ink.

Our tattoo sources tell TMZ, Adler popped in to T-Man Tattoo with his band to refresh his G'N'R tattoo -- and former
UFC champ
Chuck Liddell even made a cameo appearance.
So fresh and so clean clean.
If at first you don't succeed ... try, try again -- and with that idea in mind,
Steven Adler is going back for another season of "
Celebrity Rehab" ... TMZ has learned.

Adler appeared on season two of "Rehab" and the first season of the spin-off show "Sober House" back in late 2008, early 2009. Adler then went on to stints in real rehab centers after being ordered to by a judge as part of a DUI bust.
We're told Adler will
join the likes of
Michael Lohan,
Jeremy Jackson,
Dwight Gooden,
Michaele Salahi and
Bai Ling on the latest season of Dr. Drew's show.
The woman who's allegedly stalking
Slash and
Steven Adler found a clever way of recycling her restraining order -- cops say she wrote a bunch of crazy stuff on the back of the documents and mailed them to Adler's lawyer!

Lisa Jill-Martin Cahn was arrested on Monday by Oregon police for violating the order, after she allegedly scribbled a bunch of disturbing stuff of seven pages of the documents and mailed them off as separate letters to Attorney Eric Greenspan -- hoping they would land in Adler's lap.
In one of the letters, Cahn says she believes the restraining order is the musicians' way of communicating with her. In another, she refers to herself as Adler's "runaway kitty kat."
The letters can easily be translated as a call for help, because she asks Adler's private investigator -- David Mancini -- to "come and get me ... I'm scared and sick ... I can't do this on my own and I'm really, really, really, really, really, really scared!"
Cahn is currently behind bars at the Washington County jail and could face up to eight charges.
Guns N' Roses drummer Steven Adler is going to rehab again -- but this time there won't be any reality show cameras involved.

The former "Celebrity Rehab" star was in court today where the judge ordered him to check himself into Cri-Help Treatment Center first thing Monday morning.
Adler was popped last week for failing to complete court-ordered community service by the judge's deadline -- that punishment stems from a prior DUI bust.

We've learned Steven Adler -- former drummer for Guns 'N Roses -- has been busted (again) on a drug charge.
Cops tell us Adler was arrested on Jan. 26th and charged with being under the influence of a controlled substance -- a misdemeanor. We don't know the exact substance.
We're told Steven was released the same day at 10:50 AM on $50,527 bail (weirdest amount we ever done seen). No court date has been set.
Adler was busted last July for possession of narcotics, being under the influence and for an outstanding warrant -- and was ordered by the court to stay at the Pasadena Recovery Center.
UPDATE: 6:22 PM ET Steven's people say he was arrested because he hadn't finished his community service in the time frame given by the judge. They say Adler went to register as a drug offender -- also court ordered -- on the 26th, when cops acted on the arrest warrant stemming from the unfinished community service. He was charged with "being under the influence of a controlled substance" because that was the original charge from his July arrest.
Steven's people want to make it clear he was not under the influence of drugs.
November rain came three months early, as Guns 'N' Roses drummer Steven Adler broke down in court this AM after pleading "Not guilty" to drug charges.

Adler -- who told us he's already used up his scratch from "Sober Living" to pay for rehab and lawyers -- was busted last month for allegedly being high as a kite.
The judge said Adler must stay in the Pasadena Recovery Center -- and that clearly pissed Adler off.
So after court, our guy told Adler the BEST THING EVER -- he hoped Steven's sobriety would come before Chinese Democracy.
Steven Adler -- who was arrested for drugs and an outstanding warrant yesterday -- appeared outside the LAPD Hollywood station with his bail bondsman, and was in bright, er, spirits.
Next stop: Dr. Drew's.
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