Credit to Mojang for the armor textures.

There are many Minecraft trolls. Not that I like trolls, but sometimes it can be fun. Take your Minecraft skin, make it a 1.8 skin, and add this overlay to it. You'll look like you're wearing actual diamond armor, the only difference being that it's smaller. I've seen other peoples' versions, where the leggings are over the chestplate, which is not how Minecraft armor actually looks. This picture is of a generic skin I made to display the overlay.

Note: I have found another of this skin posted before mine. I will keep it up, though, because the other one has a Steve skin behind it. This one can just be straight-up overlayed on your skin.

2020-10-06 Update:

I wanted to keep this post because it is still relevant to older versions of Minecraft (specifically 1.8-1.13). In October 2018, the armor textures were modified to better match the other new textures in the game. That means that my new version doesn't work as well in versions before 1.13, as I used the new textures. In the spirit of the new post, I'll be including the alternate armors in the description (I still haven't produced a leather variant for pre-1.14).

As I said in my new post, I cannot recommend using these as your base skin. Please overlay them on top of another skin.

Chainmail	Gold	Iron	Diamond

Please let me know if I've missed anything or there is an issue.

All skins from this post were created using official textures.
I hold no ownership nor artistic credit over the textures used.