Hollywood actress Lindsay Lohan was reportedly left cringing when a comedy scene in Ugly Betty went wrong - and saw her standing onset in her underwear.The Mean Girls star - who makes a guest appearance in four installments of the hit TV series - is said to have suffered a humiliating incident during the filming of an episode titled Granny Pants.The scene reportedly required America Ferrera's character, Betty, to pull down the trousers of her high school nemesis - played by Lohan. But during rehearsals, Ferrera is said to have taken Lohan by surprise by removing her trousers without prior warning.A source tells New York Post gossip column PageSix, "She was wearing a G-string. And it was America's fault. "They were rehearsing the scene and America wasn't supposed to pull Lindsay's pants down - but she did. Lindsay was so embarrassed, she started crying."