There is a list of characters that separate tokens in BASH. These characters are called metacharacters and they are |, &, ;, (, ), <, >, space and tab. On the other hand, curly braces ({ and }) are just ordinary characters that make up words.
Omitting the second space before } will do, since & is a metacharacter. Therefore, your tattoo should have at least one space character.
:(){ :|:&};: