Cut the lemon in half and add it to a large pot of boiling salted water. Add the shrimp and cook, uncovered, for only 3 minutes, until the shrimp are just cooked through. Remove with a slotted spoon to a bowl of cool water. When the shrimp are cool enough to handle, peel and devein them. Keep cold until ready to serve.
For the cocktail sauce, combine the chili sauce, ketchup, horseradish, lemon juice, Worcestershire sauce, and hot sauce. Serve with the shrimp.