(I) CAN'T COMPLAIN.
(I) can't complain.: translation
(I) can't complain. & (I have) nothing to complain about.
Inf. a response to a greeting inquiry asking how one is or how things are going for one. •
Sue: How are things going? Mary: I can't complain.
•
Mary: Hi, Fred! How are you doing? Fred: Nothing to complain about.