1st of April
-----------
Not suitable! Any illness of the victim (and possible allergy to a component of the product) can turn into hemorrhoids for the joke.

YYU: A brilliant idea was born, it is a pity that it will have to wait until next year (until April 1). The bottom line: take a bag of mayonnaise (such as one with a lid), empty it and fill it with a condensate. And at the hour of "J" (at lunch, it is bish) to walk and press it out to employees in cups of coffee / tea, filled with evil laughter.
and----
When something unauthorized comes into my food, the food immediately goes out, and the joke depends on my attitude to him. His attitude will be revised.
--------

Therefore, it is necessary to pour "mayonnaise" in coffee yourself) Harmless and pleasant. And the reaction of others is invaluable.