I mean honestly anything about diet, nutrition and exercise. I started college back up to be a Dietitian with a minor in Kinesiology. I love talking about these subjects and always am down to discuss any health options. I like answering questions and being challenged on my knowledge because I'm always trying to learn and just understand nutrition as well as possible. Sadly life kind of fucked me again so I couldn't finish my course work this semester, but hoping maybe 5 years down the line I can try again. It's nice being passionate about these type of things because having the ability to continuously grow and learn a variety of ways and substitutions for meals is such a high level of serotonin.
That's a helpful topic for sure, good for you.
I feel like I already give people unprompted 40 minute lectures about stuff. Mostly Melee. Probably could give a lecture about Devil May Cry, Kingdom Hearts, or Yakuza too. I could probably manage to give a 39 minute lecture on Halo, I think I'd run out of stuff to say though in comparison to the others. Anything I like, I usually know enough about it's intricacies to talk about it for an hour straight.
I feel if you can do 39 minutes for Halo you can then bluff your way through 1 more minute, but nice topics.