Apparently, they all met up at a cafe after their schedule and ate. That is when Tiffany bought Sooyoung a cocktail and all of them had a taste of it.
Since Seohyun came late and the fact that she has never drank alcohol before, they all decided to play a small prank on her telling her to drink the cocktail saying it was a fruit smoothie. Seohyun drank the fruity top part (?) and Tiffany told her not drink the watery bottom part (where the alcohol was), but Seohyun said she'd try it and said she liked that part more, hahaha!
Tiffany then told her if she wanted to know a secret and Seohyun replied in a slightly drunk fashion, "What is it unnie?" Then Tiffany told her that the drink was really a cocktail. Seohyun was fine up until she found out she was drinking alcohol, her face then started turning red and was getting dizzy, lol.
They all said it was okay since she was with all the unnies and thought she was really cute. They even took pictures! haha~
CREDIT: NINCOMBOOB + SHADYDOLL@SOOMPI
Maybee asked who is good at drinking? Sunny chose Tiffany. Sooyoung said that Tiffany did a shot and Seohyun added that it was Tiffany that drank all of the cocktail.