the first/last to do something

be the first (person) to (do something)

To be very likely or eager to do something. You know I'd be the first to help you out; just ask me next time. She'll be the first person to admit that the program has flaws, but she still believes in it very strongly.
See also: first
Farlex Dictionary of Idioms.

(be) the ˈfirst/ˈlast (person) to do something

be very willing or likely/unwilling or unlikely to do something: I’d be the first person to admit that I’m not perfect. Mary is the last person you’d see in a pub — she hates pubs.
See also: first, last, something
Farlex Partner Idioms Dictionary
See also:
  • be the first (person) to (do something)
  • be first out of the box
  • first in, best dressed
  • for a start
  • first refusal
  • refusal
  • give (someone) the first crack at (something)
  • have (the) first crack at (something)
  • get the first crack at (something)
  • at first