(I HAVE) NOTHING TO COMPLAIN ABOUT.

(I have) nothing to complain about.: 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.