Not too bad is a modest English way of saying things are actually fine. Not too bad, thanks, oh, not too bad.
The understatement is the point, and it usually means good rather than merely tolerable. Answering not too bad avoids both boasting and complaining, which is exactly why it is so common.
1phrasenot too badA modest English way of saying things are actually fine.
“Asked how the business was doing he said not too bad.”
not too bad is a phrase.
Practised in Small Talk & Everyday Phrases