Here are some possibilities, depending on the tone and context:
Informal:
* Becca: This is a common nickname for Rebecca.
* Becks: A shorter, more casual nickname.
* Rebby: A playful, affectionate nickname.
More playful or sarcastic:
* Rebs: Can be playful or slightly mocking.
* Rebecc-a-roo: A silly, exaggerated nickname.
Slang depending on context:
* If Rebecca is considered cool or stylish: You might hear "Queen B" or "Rebby the rockstar."
* If Rebecca is known for her kindness: "Angel Rebs" or "Rebby the saint" might be used.
Remember: Slang can be subjective and might not be universally understood. The best way to understand how someone might refer to Rebecca in slang is to listen to how they talk to her or about her in specific situations.