We used to tease my boss at an arts center. His name was Eddie, yeah the one I invited who only showed up many threads later. We used to talk about his counterpart, an entirely fictitious "Edwina." Well, after he came back from vacation we told him he'd been replaced and invited him in to meet his usurper. There in his chair was the *person* we'd made out of blowing up giant balloons, then throwing clothes and a wig on "her", plus drawing a lascivious face on her. After he got over the shock of still having a job, we had a grand time celebrating with drinks and taking snapshots of Eddie and Edwina in compromising positions.
My sisters, who are identical twins, use to switch classes on their teachers, esp. on April Fool's day. The teachers, even ones who'd known for a long time, could never tell the difference.