Tuffcup is the name of the pairing between Hiccup Horrendous Haddock III and Tuffnut Thorston from How to Train Your Dragon (2010).
It is not a popular ship in the Big Four fandom, but there are still many who support the relationship. This can be considered the flipside-pairing to Ruffcup, as well as the other half of the unorthodox Twincup.
Along with his sister Ruffnut, Tuffnut would join Snotlout and would ridicule Hiccup in his failures. When Hiccup began to exhibit mastery in dragon training, Tuffnut would go on and join everyone else as a fan. When Hiccup called for the other teens to save the tribe from the Red Death, Tuffnut told him "[Hiccup] was wise to ask help from the world's deadliest weapon", talking about himself.
The origins of this shipping came when demand for a yaoi pairing amongst the group and Tuffcup was simply a result of that demand.
Note: Please add only ones that are part of the RotBTD fandom