Line a large baking sheet with paper towels. In a large skillet over medium-high heat, fry half of bacon until crisp, turning once, about 10 minutes total. Place on baking sheet, pour fat out of skillet and repeat with remaining bacon. Let cool; break each slice into 4 pieces.
In a bowl, combine mayonnaise, avocado and vinegar. Season with salt and pepper. Slice tomatoes into 6 rounds and cut each round in half.
Cut pitas in half and open pockets. Divide avocado mixture among pitas, spreading evenly inside. Fill each half of a pita with 1/4 cup lettuce, 3 pieces of tomato and 5 pieces of bacon.