I've been staffed on a old ongoing project, first day.
0. Compatibility has to be guaranteed down till IE9... ppf.
1. Front end made in XHTML+JS(jQuery)... bah, ok.
2. XHTML+JS is actually generated by PHP5.4, not a line is actually statically served... beh, funny, ok.
3. PHP files are the output of an XSLT transform of a bunch of XMLs... meh, seriously? Oooook.
4. XMLs are the product of the serialisation of a truck of stateful JavaEE6 DTOs populated magically (undocumented) with data coming from a SQL DB... WTF mode!!!
5. Session logics lives within PHP-land at point 2, front end makes ajax calls here that propagates to another WS out of our control that triggers -somehow- (undocumented) our Java backend at point 4 to generate new XMLs and then reach front end again. Kill me now.

Boss: look... it's too slow for the client, it's too heavy on our servers: fix it. Ah, and we sold 85% test coverage by October. You're the man for the job. (I'm a Node.js fullstacker and right now there's not even a testing scaffold, ofc).
Me: prod is on Linux or Windows?
Boss: RHEL7.
Me: rm -rf / as root. Done.
Boss: I know I know...
Me: ...

I think time has come...