Thinly shave the carrot using a vegetable peeler. Place in a small bowl with the vinegar. Add a pinch of sugar and enough water to cover the carrot. Let sit for at least 15 minutes.
In another small bowl, stir together the mayo and the chopped Calabrian pepper.
Open the tin of sardines and remove the backbones if desired. Gently tear into chunks and set aside.
Build the sandwich. Spread a good helping of mayo on both slices of bread. Arrange the sardines across the bottom piece of bread. Top with the pickled carrots and mixed greens. Carefully place a handful of the potato chips on the lettuce and place the top piece of bread on top.
Gently smash down and enjoy immediately.
