ET's Keltie Knight caught up with the 39-year-old actor at Vanity Fair's Oscar party following the 2019 ceremony, and he dished about he how he came up with the idea to ask his famous friends to sign his shirt.
"I found a Sharpie in the green room... and we were just chatting with some colleagues and friends and stuff and they all were quite famous. So I asked them, 'Can you sign my shirt?'" he recalled at the party, while wearing the shirt that was full of red signatures.
McAvoy wasn't gunning for any best dressed lists with the cute idea, rather he thought the proceeds of the shirt -- which was signed by the likes of Brie Larson, Samuel L. Jackson, Michael B. Jordan. Sam Rockwell, Charlize Theron, Amy Adams and others -- could go to charity.
"I thought maybe we could auction it or something [and] get some money for charity," he told ET. "... I have two charities that I work with -- Unicef and Retrak, which is a charity that works in a few different countries in Africa... and also some countries in South America as well."
"I don't quite know what we're going to do with it," he continued, before admitting, "This was off the cuff and alcohol fueled."
McAvoy detailed his idea on his Instagram Story too, where he gushed over the "incredible people" he got to sign the shirt and reiterated his charitable intentions.
"I think we'll probably try and sell it for charity. I don't know how we'll do that, but we'll figure out a mechanism and we'll figure out a destination for the proceeds of this thing and we'll do it," he assured his fans.
Additionally, McAvoy shared a snap of the signed shirt on Instagram, and quipped about how the shirt came to be signed by so many stars.
"Went to the Oscars. Presented. Got mugged by sharpie wielding celebrities. #thuglebrity" he joked in the caption. "I’m sure my shirt is going to be defaced by more of these entitled graffiti mentalists as the night goes on."