To have experienced the topic under discussion, to the point of boredom or complacency.
This phrase began life in the early 1970s, in the short form 'been there', which had the same meaning as 'been there, done that'.
Source: The Phrase Finder
We all have heard the phrase 'been there, done that' quite often on American sitcom shows. But obviously, this phrase sounds rather informal and necessitates a careful application. So, it may not be appropriate to use it in certain situations.
Is there an alternative phrase that sounds less laid-back but hits the nail at the same time?