Patinkin (notoriously hard to work with - the perfect reason why he and Patti LuPone get along so well!) used his Method training while working on the show.
He checked "Mandy" at the stagedoor and was in character from the moment he'd go back stage. One night, I had heard he allegedly threw a phone at Toni Colette on stage, along with a variety of other incidents with other cast members.
From Riedel:
"But for many of his fellow cast members, Patinkin's performance has at times been a little too intense, a little too frightening and a little too real.
Cast members say that during previews, the actor has ad-libbed bits of physical and verbal abuse, including smacking people in the head, shoving them, spitting water in their faces and making offensive remarks to them under his breath.
He has also been prone to strange emotional outbursts - at one point holing up in his dressing room and sobbing uncontrollably for four hours because he was unhappy with the show's lighting.
The actors say they were never sure what Patinkin was going to do to them on stage. One said they "walked around like we were wearing lead underwear for protection."
Patinkin's co-star Toni Collette got so fed up with his antics that she decided to get even. During the performance last Friday night, she crept up on him from behind and gave him a "retaliatory shove," according to a cast member.
After the performance, a furious Patinkin said he was quitting "The Wild Party." He did not show up for the Saturday matinee, prompting the producers to threaten him with a multimillion-dollar lawsuit, production sources said."
The rest of the piece can be found here:
http://community.tvguide.com/blog/Lonely-Ranger-Blog/700000712?month=200707