The Definitive Oral History of the Best Comedy Performance of the Year

That would be Melissa McCarthy in Bridesmaids:

Melissa McCarthy, “Megan”: I read the script and had such a weird, fast reaction to Megan. I knew exactly what I wanted her to look like, to sound like, and I got an intense feeling of “I like her so much! This will never work out!” For the audition, I wore no makeup and a bad pant. Once I look like the character, it really locks me in, even if people sometimes say, “We need you not to be repulsive.”

Paul Feig, director: We would always do an improv section during the auditions, and quickly we realized, “Holy shit, this woman is on fire.” The mistake a lot of people make in casting is they get so tied to the words and the character they wrote that they don’t see when somebody is better than what they have on the page. Melissa came in with this character that was just a force of nature. At first I was ike, “Is she playing it as a lesbian?” Then it got into all this weird sex stuff.