Place the yoghurt in a medium bowl. Grate the cucumber on a box grater and squeeze the grated cucumber with your hand to remove some of the liquid. Add it to the yogurt along with the sour cream, lemon juice, vinegar, dill, garlic, salt and pepper and stir. Serve with toasted pita crisps.
Toasted Pita Crisps:
Heat a gas grill or charcoal grill with coals. Brush the pita with olive oil and heat on both sides until toasted.