Acidic foods and drinks including citrus juice, vinegar-based dressings, and carbonated drinks directly dissolve enamel over time. Sipping acidic drinks slowly throughout the day is more damaging than drinking the same quantity quickly because exposure time matters as much as quantity.
Rinsing your mouth with water after meals, chewing sugar-free gum containing xylitol, and waiting 30 minutes before brushing after acidic foods all reduce damage. Brushing immediately after acid exposure rubs it deeper into softened enamel.