I know someone who dressed up as Siamese father-in-law and son-in-law—- I won’t go into details for fear of insulting anyone but it was HILARIOUS!!!
Someone else I know was an Arab one year. He was actually very convincing. He’s Sefardi and has a short black beard. He got a lot of weird looks (I live in Monsey, where the Arab population doesn’t exist.)
Then there was my brother the girl. He was actually extremely convincing. He wore my sister’s clothes and he would go to his friends and whenever there was someone else at the door he wouldn’t tell who he was, just that he wanted to give the shalach manos to, say, Shmuli. One of his friend’s mothers told him that this must be a mistake, because HER son didn’t talk to girls!