WE NOW have a new definition of the word “pain,” thanks to John McEnroe.

Pain is: The opening to last night’s premiere episode of Mac’s new CNBC talk show, “McEnroe.”

The opening bit involved guest Will Ferrell running amok in CNBC’s studios and supposedly disrupting the network’s noon business show, “Power Lunch,” and its anchor team, Bill Griffeth and Sue Herera.

For his part, McEnroe tagged along uncomfortably while the grotesque Ferrell invited both Griffeth and Herera to have sex with him and then announced he’d wet his pants.

The bit, which ran several eons too long, was embarrassing enough to drive viewers away by the tens of thousands (if that many were even watching in the first place).

For the dozen or so viewers who possessed the intestinal armor to stick around after that, Mac’s “interview” (if that’s what you want to call it) with Ferrell later in the show had Mac asking such probing questions as, “Where do you live?” and, “How many years were you on ‘SNL’ “?

The answers didn’t seem to matter anyway to McEnroe, who has this habit, when he speaks, of staring dazedly into the middle distance, where he makes no definable contact with his guest, the studio audience or viewers at home.

He seemed particularly at a loss for words in the show’s first conversation segment, in which he chatted with sidekick John Fugelsang, who once hosted “America’s Funniest Home Videos.”

It was clear last night that Mac intends to use tennis as a fallback subject whenever he finds himself fumbling for a topic, although it’s doubtful CNBC hired him to host a talk show about tennis.

Nevertheless, Mac took a phone call from tennis star Andy Roddick, and the two engaged in small talk about Wimbledon and Roddick’s loss in the final last Sunday to Roger Federer of Switzerland.

If you’ve ever sat and watched anyone talk on the telephone, you can guess how dull it was watching Mac sitting there with a receiver in his hand and hearing the voice of Roddick, who could have been a much better guest had he come in person.

CNBC plans to air “McEnroe” Mondays through Thursdays (with a repeat on Fridays) at 10 p.m.

The show has a studio audience plus musical accompaniment from a band led by Mac’s wife, Patty Smyth.

Last night’s premiere was enlivened somewhat by Sting, who talked about his personal “religion” – which had something to do with music and sex.