When I was in my late teens (in the latter half of the 1990s) I read a lot of Clifford Pickover’s scientific/mathematical books. There I came across my first mention of lambda calculus, exemplified by a very imposing diagram taken from To Dissect a Mockingbird by David Keenan. Years later I started to think seriously about having a tattoo of one. I thought about that for about seven years, and now I have a rendition of Turing's Theta Combinator (a fixed-point combinator much akin to the Y Combinator after which Hacker News’ mother organisation is named).
I've had it now for a few months. I’m just a bit embarrassed by owning up to having had myself tattooed to my very closest family members. My sister and my girlfriend both sport multiple tattoos, but somehow mentioning it to my father or anybody more senior unsettles me.