have dibs on
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]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.