Both hot and cold drinks cause liquid to form on the outside of a mug. This liquid will run down the mug and cause a ring stain on your leather-covered desk or couch. Remove this stain as soon as you can by cleaning it with solvents and tools that won't damage its nap or finish. Choose a nonwater-based cleaning solution for unfinished leather such as suede or nubuck.
Soak a sponge with white vinegar and wring it out so that it is wet but not dripping.
Rub the sponge over the ring stain on the finished leather until it is gone.
Rinse the area with water and immediately dry it. Don't let finished leather air dry as this can cause it to lose moisture and condition and it can also develop water marks.
Rub the white vinegar-soaked sponge over the entire couch cushion or leather table top if the water mark is still visible after you dry it.
Rinse the area immediately with water and dry it completely with a clean cloth.
Rub mayonnaise into the water mark if you can still see it. Mayonnaise contains fat that will condition the leather and remove the stain. Let the mayonnaise sit for several hours and then wipe it off.
Buff the leather dry with a clean cloth.
Rub a tan eraser over the ring mark. Don't use pink as this will only turn the leather pink. This will erase most of the stain but it may not remove all of it.
Rub an emery board over the stain to remove some of the mug ring residue. Don't rub too hard or use a metal nail file as you can easily damage the leather.
Brush the leather with a suede brush to restore the nap.