Mayim Acharonim

The 'תוס say (in חולין daf קה omud א dibur hamaschil מים) that the reason for mayim achronim is because of the salt that came from Sdom that used to be used in the past, and if one would not wash his hands after using it and would touch his eyes he could become blind). They therefore continue that for that reason, nowadays since we do not have that salt any more, people do not practice any more the minhag of mayim achronim. This opinion is brought in the Tur and the Shulchan Oruch (Siman קפא Se'if י).
In Ashkenaz that was the Psak, and therefore if someone would go and wash his hands when they were clean, just to fulfill the minhag of mayim achronim, it would be considered יוהרא.

Michael FRBSH