I frequently hear someone ask for just the salt or just the pepper and that’s exactly what they receive, one or the other. The request is not incorrect, but the response is.
The salt and pepper shakers are married and should always be passed together – even if the request was for only one.
On a side note, you may want to consider tasting your food first before deciding if it needs additional salt and pepper. Some chefs may be insulted you assumed they did not season the food to perfection.
I have also heard stories about employers observing job candidates during a luncheon or dinner to see if they taste before seasoning. They feel this gives them insight to see if the job candidate gathers all the information before making a decision.
This is clearly a black and white issue. Please pass both shakers so you do not create a shake up!