Is it okay for men/boys to wear long johns under shorts?

If it's too cold for bare legs it is too cold for shorts. Period. End of discussion. Wear long pants. certain combinations look classless and tasteless., some look stupid together and some things will make you look like you aren't too bright. Everyone with even half a brain knows when it's cold put away the shorts and wear long pants. So wear pants unless you are going for a hillbilly "people of Walmart" look. People will laugh and as I always say, if you dress like a clown then be prepared to hear people laughing at you.

well it might look funny but wear what you find comfortable

Its okay. Not the best. Probably not for if you're going out to a shoppimg centre or something. Unless you can pull it off as a certain look.