I’ve heard of the movie Deadpool, but until this thread, I had no idea Deadpool was a character. And until your comment, I didn’t realize that character wore a red suit. I can assure you I don’t live in a cabin in the woods, do watch TV (although not very often), and am obviously on the internet. I also have three kids and teach 10 and 11 year olds. My husband, brother, and students have talked about Deadpool as well, but again, always thought when the name was mentioned, it was just in reference to the movie. All this time I just thought it was the title of a movie. I also know nothing about X-Man. The only thing I know about Avatar is the characters were blue.
FWIW - If I saw this shirt anywhere, I would think it was dumb (because I wouldn’t understand anything about it, so it wouldn’t make sense to me), but finding it offensive wouldn’t even occur to me. I can see at least one of my kids catching Winnie the Pooh and the word “dead” and questioning it, but it still wouldn’t be a big deal to them or me.