The Catalan coach felt disrespected that a Guardian reporter looked away after asking him a question during his post-match press conference at Old Trafford.
Despite dominating both possession and territory, the Bavarians needed a goal from Bastian Schweinsteiger to earn a 1-1 draw at Old Trafford, with Nemanja Vidic having given the home side a surprise 58th-minute lead.
Guardiola stated after the game that Bayern had done well given that United had played with so many behind the ball but he was then upset by a follow-up question from a Guardian journalist enquiring as to whether he was "disappointed" by the Premier League club's allegedly defensive approach:
Guardiola: "I didn't say that."
Journalist: "No, I'm asking you your opinion."
Guardiola: "I didn't say that. I didn't."
Guardiola: "I didn't say that. He's [Manchester United boss David Moyes] my colleague. I respect my colleague and colleague can play like - look at me when I talk to you."
Journalist: "Are you talking to me?"
Guardiola: "Yeah, look at me when I talk to you."
Journalist: "Yeah, OK, I am looking at you."
Journalist:: "Are you looking at me?"
Journalist: "It's like Taxi Driver, this!"
Guardiola: "No, but I'm talking to you, you don't look at me, so I am trying explain."
Journalist: "Calm down, calm down."
Guardiola: "I am trying to explain. I'm trying to explain."
The eagerly-awaited second leg will take place at the Allianz Arena in Germany on April 9.