Everyone has guilty pleasures, and they're not always watching The Real Housewives. A recent Reddit thread gave people a safe space to confess the habits and hobbies they hide from their friends. Some things, like soap collecting, are nothing to feel guilty about, but pyromania on the other hand...well, you can judge for yourself.
I record myself reading books aloud. Like Berenstain Bears chapter books, Choose Your Own Adventure, Goosebumps, etc. I do the voices, edit out the mistakes, sometimes add music or sound effects. Then I listen to those recordings while doing household tasks, or especially when I can't sleep. Hearing my own voice reading helps me doze off like you wouldn't believe.
I collect Micro Machines. The classic originals from the late '80s. I have probably close to 1,000 of them and I keep them at work so my family doesn't find out and want to play with them.