The Avengers star stormed out of a TV chat with British newsman Krishnan Guru-Murthy last week (ends24Apr15) when the Channel 4 presenter started asking him about his drug abuse past.

Downey, Jr. left the room, stating, "It's just getting a bit Diane Sawyer...", referring to the veteran U.S. newswoman's reputation for probing interviews.

Now, in a new interview with shock jock Howard Stern, the movie star admits he should have known he wasn't going to have a fun time with Guru-Murthy.

He says, "First of all, I don't even know the guy's name, but I know he pulled the same garbage on (Quentin) Tarantino, and Tarantino stayed in his chair and lit him up for five minutes.

"I'm one of the guys who is always assuming the social, kind of decorum is in play, and that we're promoting a superhero movie - a lot of kids are going to see it - and this has nothing to do with your creepy, dark agenda. I just realised, too, that I'm a 50-year-old guy, I use fancy words on The Howard Stern Show, and yet I'm completely unevolved when it comes down to simple boundaries. Like, 'You know what? You're weirding me out. You are a bottom-feeding muckraker'."

Downey, Jr. insists he'll handle the situation differently the next time he finds himself in an awkward interview: "What I have to do in the future is just give myself permission to say, 'This is more than likely a syphilitic parasite, and I need to distance myself from this clown, otherwise I'm probably going to put hands on (beat up) somebody' - and then there's a real story."