texting someone while in the same house or room as them while in a group of people. usually to gossip or flirt.
you can tell when two people are cupcaking by watching them. if person A and person B are constantly looking at each other after reading a text to if right after person A sends a text person B looks at his/her phone.
Alexis: omg you can totally tell that Chris and Kelly are cupcaking!
Rachel: i know, it's so annoying. i mean COME ON are we still in High School school?!