what do you take me for?
What sort of person do you think I am? For example, What do you take me for, an idiot? This expression dates from the mid-1800s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.