Peel eggs, then slice into halves.
Transfer yolks to a small mixing bowl. Use a fork to mash up yolks.
Add mayonnaise, Dijon mustard, vinegar, 2 tsp fresh chives (or 1 tsp dried), cayenne pepper, and season with salt and pepper to taste.
Stir mixture using a spatula while pressing against sides and bottom of bowl to help smooth lumps. If mixture seems on the dry side (well chilled yolks can do this) you can add a little milk or olive oil, 1 tsp at a time.
Transfer mixture to a piping bag fitted with a large star tip. Pipe mixture into 12 of the egg whites* (reserve the last 2 for another use).
Garnish with optional bacon and remaining 1 tsp fresh chives (or 1/2 tsp dried). Sprinkle lightly with paprika to taste and a little more pepper.
Serve or refrigerate up to 2 days in an airtight container.