"Hosen" means trousers. A "Hose" would be a trouser, referring to a single pant-leg. As might be expected, needing to refer to 1 half bifurcated trousers doesn't come up in conversation often.

I think "puts on his pants 1 leg at a time, just like the rest of us" isn't used as a proverb in German. Though it could also be my German family members have never had cause to use their version of it.