7-Eleven Celebrates Birthday With Free Slurpees It's no coincidence that 7-Eleven is celebrating its birthday on none other than 7/11. From 11 a.m. to 7 p.m, you can grab a free 7.11 oz Slurpee from one of the participating locations. Celebrate the chain's 85th birthday with over 70 flavors like Fanta Lemon Creme or Coca Cola Classic. Frozen soft drinks were discovered by accident in the 1950′s when a soda fountain broke down, forcing Omar Knedlik to put the drinks in the freezer. The slushy-like drinks were a hit with customers and Knedlik later invented the first frozen soda machine. 7-Eleven agency director Bob Stanford coined the term "Slurpee" in 1967. The carbonated drinks were initially served behind the counter in stores where clerks would serve the drinks to customers.