But if you as a GM are yourself a gifted actor and entertainer and have crafted by some means a skillful script or monologue whether improvised or planned, and the players react to that NPC as being a likeable, funny, witty and so forth, then you don't have to tell the players how to react. They'll react as would be natural to a person who is likeable, funny, witty, and so forth.
Does not matter what is on the NPC's character sheet, as a GM you can only achieve that by doing the performance yourself. I can say in my notes, "The NPC is funny", but that's a useless note. The NPC is funny if the player's perception of him is that he's funny, and crafting that requires more than a note unless you are a genius comic yourself.
There is in the process of play a big difference between showing and telling, just as there is in different narrative mediums. You can never achieve the effect of telling that you could by showing, and skills and dice rolls can't replace that.