The Mischief Maker-
His Uncle George calls him his protégé. Before he could even walk properly, he could place a whoopee cushion on a chair. So from a young age, James had been labeled "the mischief maker". His father was slightly disapproving, but always laughed at the pranks, saying that he was similar to his namesake.
When James went to Hogwarts, nothing stopped him. Not Lucy, the prefect, or Molly with her silent glares of disapproval, or Louis's friendly warnings. He even sent his uncle back a toilet seat.
He let his friends in on the pranks and together they go down in Hogwarts history. But something was missing. He didn't know what.
His life was awesome and he loved pranking people.
He didn't give a damn about what the professors said. He grew up to work at the family joke shop. He even briefly considers changing his last name to Weasley, just for fun. But everyone was pairing off. Teddy had Vic, Dom had Ralph, Louis had Max, Molly had Jason, Lucy had Limon, Fred had his Iz, Roxie loved Lysander, and there he was all by his lonesome self.
He was worried that nobody will want to stay with him because he pranks too much.
But surely that wouldn't happen because Uncle George found Aunt Angelina!
Maybe he just has a defect.
And then he meets her. And he knows that Trisha Jameson, in all her red-headed glory is The One. So he tones down his pranks and tries to please her.
Then he sits down on his first date to find a whoopee cushion there and he freaks out.
Turns out she likes pranks.
So the ongoing prank war between them never stops and James knows that his Mischief Making will never end. He can't believe he tried to stop it in the first place.