if I’ve told you once, I’ve told you a thousand times

if I've told you once, I've told you a thousand times

I've reminded you about something many times. Typically said in annoyance or frustration. if I've told you once, I've told you a thousand times: don't leave your wet towels on the floor! You need to put out the trash on Tuesday mornings—if I've told you once, I've told you a thousand times.
See also: if, thousand, times, told
Farlex Dictionary of Idioms.

if I’ve told you once, I’ve told you a thousand times

phr. I know I have told you many, many times. If I’ve told you once, I’ve told you a thousand times, don’t lean back in that chair.
See also: if, thousand, times, told
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • if I've told you once, I've told you a thousand times
  • many a time
  • many's the time (that)
  • many and many's the time (that)
  • many 's the time
  • is it
  • think on
  • think on (someone or something)
  • have got a leg up on (someone)
  • languish in