The worst project is the one I am currently working on. I didn’t build it but have to manage it, because... Reasons.

The projects is made on Core PHP(red flag right there).
But when I dig in I get to see there is no authentication used in any of the REST service. Yup. What's the fucking point of login if you are just going to update profiles based on user_id you Twat! The querying used is simply mysql_query (I have to say I expected that).
No relationships defined in the Mysql table structure. No migrations.
There is an upload feature which is forcing the image to be saved as jpeg, therby corrupting the images being saved on the server.
No security, terrible logic, no classes, terrible architecture.

And I am the chosen one to maintain this shit!

Truely, FML!!!