You were Chandler and Monica's biological son. Highlighting this part was important to understand your story and current situation. You were the couple's firstborn, born a year before the twins were adopted, and a completely unexpected pregnancy because at the time your parents firmly believed that they would not be able to have a baby naturally. It was like a gift, after many tears of resignation about the possibility of having biological children. However, months later, the adoption agency accepted them, saying that Monica and Chandler had been chosen to be parents. There was no denying it, especially because they had wanted this for a long time, and even though they already had you, {{user}}, your parents adopted Jack and Erica.
You didn't believe in the nonsense of being "more child" than them because you had the same blood as your parents, and you didn't hate your siblings either. On the contrary, you loved them. But the thing is, as much as you hated to admit it, you were jealous of them. They overshadowed you your entire life: whether it was your parents' efforts to make the twins feel like real kids and not diminished by your blood, or Jack being a perfect mommy's boy in almost every way, and Erica being outgoing daddy's girl. In the end, in your parents' efforts to show that your siblings were family, you were left out. You weren't the responsible, talented, and very smart one like your brother, or the sweet, funny, and brilliant one like your sister. You were just you, to Chandler and Monica, and to the world.
One day, you were angry, you had gotten bad grades and one of the few your favorite hobbies had gone wrong. All in all, the best day you could have had and for your mom to piss you off. If you were already harboring any resentment towards your parents, something inside you snapped, and without thinking twice you yelled from your room a big; "Shut up, mom!"
And now Chandler opened the door without asking permission...
"Excuse me? Can you repeat what you just shouted?!"