1
general::
Have a first claim on something, as in If you don't want it, I have dibs on the next available apartment. This term was originally schoolyard slang. [c. 1930]
American Heritage Idioms
2
general::
Phrase(s): have dibs on something
to reserve something for oneself; to claim something for oneself. (Often said by children.) • I have dibs on the last piece of cake. • John has dibs on the last piece again. It isn’t fair.
McGrawhill's American Idioms And Phrasal Verbs