My top five from this (all valid):
- ":(){␣:|:&␣};:"@example.com # fork bomb
- 👉@👈 and poop@[💩]
- "@"@[@]
- c̷̨̈́i̵̮̅l̶̠̐͊͝ȁ̷̠̗̆̍̍n̷͖̘̯̍̈͒̅t̶͍͂͋ř̵̞͈̓ȯ̷̯̠-̸͚̖̟͋s̴͉̦̭̔̆̃͒û̵̥̪͆̒̕c̸̨̨̧̺̎k̵̼͗̀s̸̖̜͍̲̈́͋̂͠@example.com
- fed-up-yet@␣example.com␣ # ␣ = whitespace
My top five from this (all valid):