It wasn't some kind of protest... I just completely forgot until I got to the self service tills and saw my face in the security screen !
I put it on straight away, yet no one in the shop had said anything to me, and I'm still alive, so I guess that's a good thing?
Have you ever forgotten? I feel so naughty now!
EDIT: Even the little 'Help' smiley looks like its putting on a mask!