Tantrum is an energy drink which according to Future Ted has "the highest caffeine level legally available over the counter". In college, Ted and Marshall drank this during the road trip from Wesleyan to the pizzeria Gazzola's. The drink brought on a severe caffeine high and according to Ted, made him colorblind for two weeks. (Duel Citizenship)
Notes and Trivia
Tantrum might be a reference to the Norwegian citrus soda Urge made by Coca-cola exclusively in Norway. Urge is a high caffeine energy soda. It's most likely, though, a reference to "Jolt Cola", a soft drink available in the US and Canada in the 80's and 90's that boasted "All the Sugar and Twice the Caffeine", or Surge, a highly caffeinated citrus-flavored soda popular in the 90s. It may also be a reference to Mountain Dew which shares its characteristic color, caffeine, and hardcore marketing but most likely the green flavor of Jolt.