I like to run in shorts if I can.

For the last month or so we've been getting snow on and off. So I started running in trousers (and a hat and gloves). But then after one run, I went to take a pee and my groin extremity was very cold -- I didn't have any feeling in it and I'd say I was only a degree or two away from frostbite. So next I got a willy-warmer. And lastly I got a pair of briefs to put on over the willy warmer.

But today it's 51 fahrenheit so I'll just run in trousers and a hoodie, and probably take off the hoody after about 15-20 mins. No need for the extra groin stuff. Hat and gloves not essential.