Ask him about his first invite to the big league side of things, and Rienzo talks about the amazing opportunity. Ask him about playing for Team Brazil in the World Baseball Classic, with the 24-year-old native of Sao Paolo starting Game 1 of Pool A against Japan in Fukuoka, and Rienzo raves about the excitement in his country for a sport previously missing huge popularity.
And ask him about Hall of Famer Barry Larkin managing Team Brazil and a broad smile crosses his face with the answer coming before the question is complete.
"Oh, Barry Larkin is awesome," said Rienzo, with his Brazilian accent still fairly evident. "He helped the team a lot. He's great. He's a fun guy."
During a six-minute interview, Rienzo puts forth quite a few "yes sir" and "no sir" in his answers while keeping that smile. There might be fast-rising pitching prospects having as much fun as the right-hander during Spring Training, but it's a safe bet that none are having more.
This happiness hasn't quite been universal for Rienzo as part of the White Sox since signing as a free agent on Nov. 17, 2006. That high energy was temporarily replaced by heartbreak and shock last April 26, when Major League Baseball announced that Rienzo received a 50-game suspension after testing positive for metabolites of Stanozolol, a performance-enhancing substance.
Approaching one year since the announcement, the White Sox don't say much about the specifics of the suspension but stand firmly in Rienzo's corner. They have become a second-chance organization for controversial figures who have thrived on the South Side of Chicago. Moving past a mistake made by a quality kid such as Rienzo was an easy decision.
"We kind of just take it for what it is and just kind of move on," said White Sox assistant general manager Buddy Bell of Rienzo's misstep. "In Rienzo's case, he made a mistake and certainly he's bounced back really well."
"He came down to extended and kept himself moving," White Sox Minor League field coordinator Kirk Champion said of Rienzo. "He maintained his throwing and carried it right back on the mound. In the fall and the winter, he made up his time."
Testing positive is not a mistake that Rienzo brushes aside lightly. Rienzo bought a supplement in a Brazilian store that he believes unknowingly had the banned substance. If it didn't contain the substance, it might have been mixed in another vat containing remnants.
Rienzo said that he would never pick something "that I know is illegal." He also understands there are ways to check supplements in the future before using them.
"Yes, it's my fault. I'm responsible for that," said Rienzo, sitting in front of his locker at Camelback Ranch. "I never take something and say, 'That is bad. OK, let's go try.'
"I try to forget and keep doing my work. It's my fault. But now it's time to keep going."
This unexpected 50-game break didn't stop Rienzo's momentum.
Between stops at Class A Winston-Salem, Double-A Birmingham and Triple-A Charlotte, Rienzo posted a 7-3 record with a 2.53 ERA over 18 starts. He fanned 113 over 103 1/3 innings.
In the Arizona Fall League, Rienzo struck out 24 over 24 2/3 innings during six starts. He became the talk of the AFL and not just by the White Sox.
"He's got sink to his fastball, he's got a good breaking ball, above average velocity. Then he competes," Bell said of Rienzo's Major League qualities. "The one thing that he's had to work on more than anything is he has instincts but just because he hasn't played a whole lot, he's had to kind of, he gets a little bit analytical with his delivery and stuff. We ask him to be himself and just let it go."
"There were some nights when he's really, really competitive and some nights he falls backwards," Champion said. "But it's not taking him as long to recover. Where maybe before it was a game or two, now it's an inning or two or a pitch or two. That's the nice thing to see. He's starting to get a real feel for his repetition. He's caught people's eyes."
Although Rienzo played baseball with his brothers growing up and was influenced by his mom, who played softball, Champion points out that he didn't have the solid base other young players possess when joining the organization. He's developed those basic skills as he worked on not trying to be too perfect with each pitch.
Fifty-seven walks over 128 innings in 2012 show Rienzo remains a work in progress, but an eager participant to learn.
"I'm just trying to throw more strikes because sometimes I'm ahead in the count and I tried to throw so perfect," said Rienzo, who features a fastball, curve, slider and change, while working on a cutter. "Last year I tried to [get] more contact and tried throwing over the plate and see what happens."
The 2013 White Sox rotation looks set one through five, and actually six if Hector Santiago is included. But Rienzo has put himself into that next group of three or four if a big league starter is needed.
With last year's mistake put firmly in the past, the good-natured Rienzo once again is having fun with his push to join Cleveland catcher Yan Gomes as the only Brazilian-born Major Leaguers.
"Don't mistake his kindness as a weakness, because he's really a tough kid," said Bell of Rienzo, who threw two innings in Thursday's Intrasquad game. "It's unusual too because he hasn't played a lot of baseball. The kid has really kind of put all that other stuff behind him. We are real happy for him. He's a great kid."