It is rather silly that you ask us if you can wear denim over cycling shorts because you know the answer...YES and you can wear whatever you want. The problem with wearing denim or any fabric that fades and wears easily is a sweat ring around the rump. Certain fabrics don't do well and deteriorate from rubbing and sweat even with the bike shorts worn under. I have ruined two pair of pants already so I just wear designated pants and skirts.