The complaining customer is a non-Seeker who ordered a double cappuccino in a coffeehouse of Venice, Italy. He complained to Sophie Casterwill, who was temporarily working there at the time, that his double cappuccino was not hot enough, calling her a dimwit for this action. Lok Lambert reacted by using a Boltflare spell on the cappuccino, after which the customer burned his tongue. This event is most likely the reason that Sophie and Lok were fired. S1E14