For the Parsley Sauce: In the bowl of a food processor, blend together the parsley, garlic, vinegar, chili flakes, sugar, 1 1/2 teaspoons salt, and 1/2 teaspoon pepper until smooth. With the machine running, gradually add the olive oil until incorporated. Place half of the mixture in a medium bowl. Place the remaining mixture in a small serving bowl. Cover with plastic wrap and refrigerate until ready to serve.
For the Beef Pops: Place the beef in the medium bowl with the parsley sauce. Toss well until the beef is coated with the mixture. Cover and refrigerate for 3 hours.
Place a grill pan over medium-high heat or preheat a gas or charcoal grill. Thread the skewers starting with a piece of pineapple, then a cube of beef. Repeat with another piece of pineapple and another cube of beef. Continue with the remaining skewers. Grill the skewers for 2 to 3 minutes each side (for medium rare) or until desired doneness. Season with salt and pepper.
To serve, arrange the Beef Pops on a serving platter. Drizzle with the remaining reserved Parsley Sauce or serve the sauce on the side as a condiment.