If the investor is spending his precious time meeting with you, then I assume he has at least some interest in your event. If that's the case, then in my opinion, yes it would be a nice gesture and appreciated. Good luck with your pitch!

It's a nice gesture, but don't expect it to influence his investment decision. Also, don't expect him to ever wear it. He might. He might not.

I work in NY with many startups. Everybody likes freebies, even investors. He or she may end of giving it to one of their kids or to another person, but it is a nice gesture.
When we hold healthcare events people from all walks of life fill their bags full of chotskies. And I can tell you that when we hand out t-shirts they go quickly.

My feeling is if you are going to give something let it be something that a person would not throw out and really brands you in a way that makes you stand out and be special. A tee-shirt to me is common and if it's branded it's not likely I would put it on my body.
However if you gave me a water bottle from S'well with your logo on it - that puppy would be with me everyday and I'd be thinking about the fact that you were someone who cared enough to give away something really special.
Just my thoughts....

hahaha. nice.

This depends on your relations with him. If he has already invested in your company, sure!

If you are looking for an investment from him, think well.

If he is a cold guy, who minds his business, it could be good to refrain from it. But if he is warm, friendly and really likes your company, why not! :)