Some advice for when Willie Nelson slides off his sneakers personalized with the word "Texas": Don't mess with him.
The country music icon who turns 81 this week received his fifth-degree black belt in the martial art of Gong Kwon Yu Sul on Monday night, parking his tour bus outside the Austin studio of his instructor who began teaching him two decades ago.
Nelson didn't show off his chops but Grand Master Sam Um assured a packed room that the "Red Headed Stranger" could hold his own against anyone. As is typically the case wherever Nelson goes, other celebrities were close: this time Austin resident Lance Armstrong tiptoed past parents of other students to see his fellow Texan honored.
"Honestly, I was surprised to be getting this degree," Nelson said on his bus before the ceremony. "I don't know what else is out there. I never thought about anything beyond second-degree black belt."
Nelson's birthday is Wednesday -- though he's claimed before that the date is really April 29, a day earlier. He said a doctor gave him a clean bill of health earlier Monday during an annual exam.
The singer gives martial arts a lot of credit for that. Although off stage he's more famously known for more mellow interests -- like smoking pot -- Nelson said he stays physical whenever possible. He's also a runner and avid bike rider.
"I'm pretty healthy at 81. I think a lot of it has to do with the exercise that you do," Nelson said. "I think martial arts is one of the best exercises you can do. Mentally, spiritually, physically, everything. I'm sure that's helped."
Nelson cinched his black belt -- personalized with his name -- around a black robe and wore his signature braids behind his head. It was a more low-key affair than usual for the lionized singer: Just this past weekend, Oscar winner and fellow Texan Matthew McConaughey inducted Nelson into the Austin City Limits Hall of Fame at a blowout concert.
When Nelson initially showed up to his studio, Um said he worried about the musician's heart because of his age. Then the instructor got a glimpse of his lifestyle over the next 20 years.
"He has more stamina than I do," Um said.