A wall-stache is a mustache that either suddenly appears on one's wall or grows over a period of time. Wall-stache's are known to come in varying colors, shapes, and sizes, but the most common colors are brown and black.
Anyone who's wall is unable to grow a stache can obtain one simply by purchasing a fake mustache from a joke shop or costume bazaar. (caution, this fake stache on the wall will result in your wall losing any self respect and/or masculinity)
Me: Ah!, I've noticed that your wall has grown a handle-bar mustache.
Person who's abode I have entered: Yes, this is a rare Wall-Stache, they usually grow in stache colors of black and brown; not in the peppery tone mine has
Me: This is quite a feat your wall has accomplished.