Combine Mayo and vinegar until the mixture tastes sour and is thin. Add pepper, salt and other spices as desired. Grate onion directly into the sauce (try to get the onion juice and grated solids in. Dice cucumber and add to sauce. Hand smash eggs and introduce to sauce. Thinly slice potatoes and stir into sauce after a few slices to keep potatoes from sticking to each other.
Chill for a few hours and serve cold.