Wow! Mid 40s in only underpants is pretty chilly, especially since riding a scooter doesn't involve much effort. When I'm riding my bicycle I'm generating a lot of heat. If I'm cold I can just pedal faster. When I ride my motorcycle in cold weather I just sit there and suffer.

My record for my motorcycle is 4F. I think I wore every piece of clothing I could fit underneath my leathers, and still was freezing cold. I had to avoid the faster roads because above 35 mph I would get the worst ice cream headache I could imagine. Generally I stop riding the motorcycle when temps drop below freezing. Even in the 30s and 40s though I still have to dress pretty warm to keep the temps tolerable.

On my bicycle my record is -14F. Outside of my hands and feet getting cold (for which I've yet to find a good solution) I was just fine once I warmed up. The first mile after I leave home is all downhill, so that can be a bit nippy but then once I start providing the momentum I stay plenty warm and actually have to be careful not to sweat too much. I find it really doesn't take a whole lot of clothing to stay warm on a bicycle.