I've never flashed my mum, however I think I have a similarly silly story. My coming out to her was quite hard and we didn't speak for a few years, that context is important because she didn't see the changes until after they had all happened.

Anyway, fast forward to the second time seeing her again in person. I went out for dinner with her back in my hometown, and brought my girlfriend along. We were back at my mum's having some drinks out on the back deck, and I excused myself to the spare bedroom because I desperately needed to take my bra off, which had heavy underwire. Now, my mum is particularly well endowed, and while I pale in comparison I'm still fairly big for a trans femme (DD/E cup). I needed to go to the toilet but I stopped back past the deck, waggled my tits in her direction and said "I guess I have you to blame for these two back problems" and walked off back inside.

Apparently my girlfriend and step-dad were laughing their heads off while my mum turned beet red 😂

I don't live with them since last fall, but I go back on occasion. Getting the space to just exist in my own home has given me room to start validating my own identity as trans. I have thought about it, and I'll probably start writing up something tomorrow to send to them. I feel like I have a lot of mental inertia, which I have to overcome. I've hid this for 11 years, if not longer, with occasional blips of just not being able to do it and not feeling understood as a result. Overcoming this inertia by re-engaging with it has been hard, because I get really anxious every time I have to confront it, but doing breathing exercises, listening to trans-affirming ASMR, and meditating feels like it's helping.