I have noticed that there had been random joint textures appearing on everyone lately, including me. Namely, a texture on the back that resembles either a pillar, tower, or some other sort of rather phallic object, and a celtic tattoo on the left chest.

Is this a joint texture promotion event of some sort? Or is it an issue with my client?

If it is intended, please give an option to hide it. It is extremely distracting, especially the one on the left chest, as it interferes with my playing by turning the joint highlight a different colour and making all states of the joint look like relax / force to me...

It's a known bug.