1. I push supermarket trolleys with just one hand, the right one. This took its rise when I sustained a shoulder injury about twenty years ago, and it became a habit.
2. When I encounter meaningless random large integers (such as serial numbers on bus tickets) I factorize them, and get absurdly pleased if I find particularly large prime factors.
3. I count up how much spam I get on my longest-established email address, and put the results into a little graph.
4. I flip my pillow each night as I go to bed, so I rest my head on the surface which was underneath the preceding evening. It never occurred to me that this was weird, but I'm assured by an independent observer that it is.
5. When I remove my shoes I stand them together, heel-to-heel, toe-to-toe, with the long axis of the shoes parallel to one of the walls of the room I'm in. I get quite edgy if I don't have the opportunity to do this, or if someone I'm with does't do the same. Oddly, I'm okay if I go into a room where there are shoes already misaligned -- it's the act of placing the shoes, not their current arrangement.
The great theory is that I tag five people to do this, but I have a bonus weird habit, which is to subvert instructions like this and do something different.
I'm just about to have a pizza. So if you're about to have, or have just had, a pizza then please scare us with five of your weird habits.