Hey! Keep Your Debugger Outta My Code!!
Want to make someone's debugging life a little confusing? Do this:
[System.Diagnostics.DebuggerStepThroughAttribute]
public class NoDebuggersAllowed { }
Any methods added to NoDebuggersAllowed will not be debuggable because of that attribute. A co-worker was going nuts because his breakpoint on the constructor was never getting hit. It took me a while before I saw that the attribute was on the class. He didn't add it; the class was generated from some code generating tool and thought it would be a wonderful idea to confuse the hell out of someone by not letting them step into the internals of the generated class.
I can see where this attribute has some benefits, but the next time you're sure you've set a breakpoint that should be hit and it isn't, look out for DebuggerStepThroughAttribute!