1
general::
Phrase(s): (I) can’t complain. [and] (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.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Used as a response meaning fairly good or well, to questions such as "How are you?" or "How is business?" For example, How've you been?? Can't complain. This term means that nothing serious is wrong. [Mid-1800s]
American Heritage Idioms