A characteristic of obese people, especially women, where their excess fat creates a protrusion in the front as large as (or larger than) their posterior, hence the "double bubble".
"Whoa, check out the double bubble on that hot mama with the cat sweater! She must eat a lot of KFC!"
When you get a boyfriend, become completely infatuated with him, and forget your other friends. Your boyfriend then becomes your only friend because you only ever hang out with him.
After Katie started dating Mark, she got sucked in the boyfriend bubble and lost all her friends.