Not having any testers.

Management assuming we devs can test our enterprise app using only auotmation tests.

Big surprise coming when we release.

In C# using "this."

WHY? It doesn't help with readability. It just clutters up the code and adds nothing.

It should never be a required prefix.

What makes it worse is, Visual Studio greys it out because its not required!

Then there is stylecop. This got enabled on our project which generated 3000 build errors because of missing "this."