Jonas Bros.

Sorry you creepy weirdos ... Joe Jonas did NOT record a raunchy sex tape with his Swiss model GF ... despite reports to the contrary ... Joe's rep tells TMZ.

Reports have been circulating that Joe -- who once wore a purity ring espousing his virginity -- filmed himself doing the nasty with gf Blanda Eggenschwiler while under the influence of pot and alcohol. The reports claim the sex footage features some crazy BDSM stuff, including paddles and ball gags.

But Joe's rep tells TMZ, it's total BS ... no such tape exists.

A Jonas Brothers fan has sued the group, claiming they're so popular, she was crushed during a concert by crazed groupies.

Ashleigh Johnson filed the lawsuit -- obtained by TMZ -- in which she claims she was at The Grove in L.A. back in May, 2010, watching the boys perform an early bird special (3 PM), when she was pushed by an uncontrolled crowd against a guard fence.

Ashleigh says she was "agonizingly crushed" into the fence and suffered serious mental, emotional and physical injuries as a result.

Ashleigh -- who didn't ante up her age -- is suing the group as well as Caruso Management, the folks behind The Grove.

This video ... IS SOOOOOO SAD!!!!

A passionate Jonas Brothers fan waited outside Katsuya in Hollywood last night -- in the cold and the rain -- for a moment with her hero, Kevin Jonas ... only to learn what rejection feels like.

It was SOOOOOO SAD!!!!

FYI -- Kevin DID take pics with a bunch of fans as he left the restaurant with his wife ... trying to please everyone ... but the superfan got lost in the crush and never got a chance to pose with her hero.

Still, SOOOOO SAD!!!!

Joe Jonas checked into an emergency room in L.A. while doctors inspected his abs -- for severe stomach pains -- 48 hours after Joe did some late night partying in Chicago.

A rep for Joe confirms he went to the emergency room at Children's Hospital L.A. on Sunday. We're told Joe was only at the hospital briefly ... and it's not clear what was wrong with him.

One potential hint -- on Friday night (into Saturday morning) Joe was out at a Chicago hot spot Board Room Nightclub (above) partying ... and performed the next night in Chi-Town.

Whatever the problem was ... Joe felt good enough to eat out -- we spotted him and his bro Nick leaving Katsuya last night. Sushi after stomach troubles? Risky, Joe.

Nick Jonas, 18, and his older girlfriend Delta Goodrem, 26, enjoyed an adult unchaperoned vacation in Mexico this weekend.

Sources tell TMZ ... Alex Welch was on the receiving end of Demi's blow. Welch is a backup dancer on the Jonas Brothers Live in Concert Tour. She was also a member of Beat Freaks, which got the runner-up title on season 3 of "America's Best Dance Crew."

We're told Welch -- who had a pretty nasty shiner from the incident -- has been talking to lawyers and is considering legal action.

Sources close to Demi say she feels "awful" about her behavior and took personal responsibility for it by leaving the tour and seeking help.

A source connected with the tour tells TMZ, "There are no plans to replace Demi for the remaining six days on the Jonas Brothers Live in Concert tour."

As TMZ first reported, Demi decided to leave the tour and seek help for "physical and emotional issues" at a treatment facility.

In a statement to TMZ, the 18-year-old singer's rep says, "Demi Lovato left her tour early this weekend in order to seek medical treatment for emotional and physical issues she has dealt with for some time."

We're told Demi is not seeking treatment for drug use.

The statement continues, "Demi has decided to take personal responsibility for her actions and seek help. She is doing just that."

The rep concludes, "[Demi] regrets not being able to finish her tour, but is looking forward to getting back to work in the near future."

Sources close to Lovato tell us the singer was in a physical altercation with a female member of her tour recently ... which was a "catalyst" in her decision to seek professional help.

Jesus loves your skinny jeans.

Purity rings aren't the only ones the 20-year-old can rock.

TMZ has learned the teen Disney idol was on the hunt for the perfect timepiece for a special friend -- if you believe the rumors, that friend is Nick Jonas. She picked it up at a jewelry store in the Northpark Mall in Dallas.

We're told she got the watch engraved with the phrase "Check the time ... I love you right now" -- and then personalized the box with a line from a Roy Croft love poem: "I love you, not only for what you are, but for what I am with you."