"That city put its arms around me and many other players, man, in a way that's tough to describe," he said. "It's a special place for me."
So obviously Theriot has reversed course since signing with the Cardinals the following season, in 2011, and changed his mind about telling St. Louis media how great it was to be "finally on the right side of the rivalry," right?
"No, I've not," Theriot said. "Because at that time, the St. Louis Cardinals were writing my paycheck. And if I'm anything, I'm smart."
Theriot, the only starting shortstop for multiple Cubs playoff teams between Billy Jurges in the 1930s and Addison Russell in 2015-17, understands the complicated nature of the Cubs-Cardinals rivalry perhaps as much as anyone.
A fan favorite in Chicago for Dusty Baker's and Lou Piniella's Cubs teams, he caused a stir with the "right side of the rivalry" comments when switching sides in 2011, stood by his comments upon his much publicized return to Wrigley Field, and then won a World Series that year with the Cards - followed by another in his final season, with the Giants, in 2012.
Theriot - who had the game-tying hit in the ninth against the Cubs in 2011 that led to Carlos Zambrano's famous "we stinks" rant - is just one in a long line of players to experience both sides of one of the longest-standing rivalries in the sport, from Hall of Famers Rogers Hornsby, Dizzy Dean and Lou Brock to current-day All-Stars Jason Heyward and Dexter Fowler.
Just last year a months-long fan-agitating stir was started by Cubs third baseman Kris Bryant joking that St. Louis "is so boring."
That almost put Theriot's rivalry-stoking comments in 2011 to shame - though Theriot got booed at least as loudly upon his return to Wrigley that year as Bryant did in his first appearance in St. Louis last year.
Nothing new for a rivalry nearly 140 years old that took on an elevated tone when the Cardinals started winning championships under executive Branch Rickey's direction in 1926.
Just ask former Cardinals hero Jim Edmonds, who signed with the Cubs 12 years ago this month with significant doubt about how much he had left in the tank - and then stabilized center field while going on a post-May tear that helped the Cubs to the National League's best record.
He got a standing ovation before his first at-bat as a Cub in St. Louis - then booed with the rest of the Cubs the rest of the game.
"Jimmy was just a wonderful teammate to be around," Theriot said. "I still talk about his opposite-field power; in batting practice he would hit balls out to left field almost easier than he did to right field. Just bringing that winning mentality over, it's a different perspective."
Until the Cubs finally broke through to win the 2016 championship, that was distinct.
"Being in both cities and playing for both teams it was a little different, because in St. Louis with Tony [La Russa] and those guys, the whole ‘can we win' question was never a question, because they had done it and repeatedly done it. It wasn't an ‘if.' It was almost like a ‘when' - ‘when are we going to put our foot on the gas pedal and get this thing going and win this whole thing.'
"So Jimmy kind of brought that mentality and that aspect to the clubhouse, a calming feeling."
The Cardinals' championship in 2011 was the most recent of their National League-record 11.
But that team wasn't as good as the Cubs' 2008 team, said Theriot, despite its first-round loss to the Dodgers - Piniella later admitting the weight of 100 years contributed to playing tight.
"I agree with Lou," Theriot said. "It got real tight that year in '08. And I still say to this day, that was the best team I ever played on. That 2008 team was the best major-league team that I ever played on, top to bottom - '11 was pretty close."
Eight years later, at home with his son Houston "fired up" and sitting next to him in a Cubs jersey, Theriot was "locked into every game" of the World Series the Cubs finally won in 2016.
"It was pretty emotional for me to watch those guys," he said. "I'm just so happy for the city, for all those die-hard Cubs fans that live right there around the stadium, that have the memorabilia on their windows, and you see the old-timers that wear pins all over them - it's a dream for those guys to experience a championship.
"I know I wasn't part of that team, but I had some pride when they won."
Ryan Theriot understands Cubs-Cardinals rivalry perhaps as much as anyone originally appeared on NBC Sports Chicago