Some people don't seem to notice they are still wearing one when off the bike for some time.
Well, I did go out on a training ride, the other weekend and forgot I didn't have a lid on. I wear a skull cap to absorb sweat always, so the helmet directs air flow and absorbs it - works amazingly, no drips. I'd put the skull cap on, fitted shoot to bike and went off. Only realised 5 miles later when my head was feeling hot, touched 'head/lid' - oh no lid....
Get this, I was on a gravel/road ride, and by pure luck, I'd not headbutted a few branches yet - that's what the lid does...
It has to come off the minute I stop though, no way would I leave it on - you look a complete plonker off bike anyway.