I do a couple things that probably should go with people substantially younger than I am.
I have fake conversations on my phone when I'm bored in public. They range from the benign to me pretend arguing with someone, I never say any details of what it's about, but I derive a lot of amusement from walking back and forth and being expressive in my conversation to no one.
Most patterned floors I cross I make up rules for what tiles/colors I should or shouldn't step on. I try to be coy about it while doing it, but I'm sure taking random unusually large steps, tiny steps and right turns on some surfaces in some places has made me look a bit out of it.
And I watch a good amount of cartoons. Not just anime or more adult oriented things, but I drop by some stations to see what's on and will sometimes stick around for a cartoon show rather than go watch the news or one of the information channels.
I like to assume this means that I'm in touch with my inner child and understand what I find enjoyment in, and not that I'm an unbalanced human being.