Wow- I have never seen this before! Marc said this was definitely unscripted. At least they were able to play it off for laughs!
Back in the 90's Burt Reynolds was a guest on The Tonight Show (with Jay Leno), and clashed with another guest, Marc Summers, when he felt "dissed" by Marc. And then hilarity (uh, tension) ensued!
Read more about the incident here, and see it below!