The Oscar winner has been grooming his facial hair since March (14) in preparation for the Shakespeare in the Park production in the Big Apple's Central Park, but he admits the bushy white beard hasn't won him many compliments.
During an appearance on America's The Tonight Show Starring Jimmy Fallon on Thursday (17Jul14), he said, "It's making me feel nice and old... (but) not everybody likes it.
"If you're a recognisable person, you walk through town with a kind of swagger, but with my beard now... I was crossing a New York street and this guy had just slowed down (in his car), looking for an address or something, so I crossed in front of him, he saw me, he sort of sped up, chased me off the street, rolled down his window and said, 'Why don't you f**king shave?'"
Lithgow was too shocked by the unexpected insult to respond, but he decided to use his Tv interview to send a message back to the rude driver.
He explained, "That's why I did (this talk) show, so in case he's watching, I can say, 'The Tonight Show, King Lear, that's why I didn't f**king shave!'"
Lithgow will star opposite Annette Bening in the open-air revival, which begins its limited run on Tuesday (22Jul14), and he can't wait to hit the stage as Shakespeare's tragic royal, adding, "It's been the answer to the question, 'What role would you want to play?' for all these years, and now I'm playing it!"