Can men wear leggings to work, and if so, with what?

Yes! All of the above apply for men. Please consider that, if your workplace is primarily socially conservative, you may feel unsafe or ostracized. However, as long as your "bits and pieces" are covered, there should be no reason why you can't wear leggings. (They are very comfortable.) Here's an outfit recommendation: a top that goes below your hips (i.e. an untucked button-up), some nice loafers or non-sneaker footwear, with a more formal or neutral colored sweater (doesn't have to be long) for a more "casual professional" look. If you'd like, add a brighter accessory to draw attention away from your legs (i.e. a brightly colored scarf, blocky necklace, etc.).