I didn't really celebrate per se. But I remembered it was 10.10.10. I looked for cool events and was dismally disappointed. There was a vague eco-friendly scavenger hunt in a nearby park that I walked past, but... really?
I drank a toast to my senior maths teacher, who used to do something cool (cool for a maths nerd) with the date every day and hoped he was appreciating the day somehow. I also remembered thinking as a teenager that one of these 'cool' dates would be a good time to have a baby. Funny those moments, no?