In a blender or food processor, combine lime juice, crushed garlic, orange juice, cilantro, salt, pepper, olive oil, jalapeno, and vinegar. Blend for 30 seconds until almost smooth.
Place the flank steaks into a resealable bag, and add the blended liquid. Seal it up tight. Make sure all the meat is exposed to the marinade, squishing the bag around to coat. Refrigerate for at least 2 hours, or overnight.
Heat an outdoor grill to high heat.
Remove the flank steak from the marinade, and discard excess marinade. Cook on the grill for 7 to 10 minutes per side.
Once done, remove from heat and let rest 10 minutes. Slice against the grain, and serve.