Consumerism, yay? [T-shirt proliferation is a big fashion waste problem.] Though to be fair, sounds like a lot were bought second hand, gifted, resulted from participating in events. If you're going to ask a person about their t-shirt collection, make sure they've lived an interesting life, so you get nifty anecdotes along the way. Approachable writing style.
Pink shirt with row of ukeleles from Hawaii, and green winged octopus were my faves.