Chop the pickles, celery, and onion into small pieces.
Drain the sardines, place them in a medium bowl, and break them up with a fork.
Stir in the mayo, sriracha, lemon juice, Dijon mustard, and black pepper until well combined. Adjust the amount of sriracha to taste.
Serve chilled with crackers as an appetizer or in a sandwich for lunch.
