This one candidate had been allowed to skip the phone screen, and phone screens would likely have filtered them out. Candidate used Java and claimed to be deeply familiar with it. Obviously this isn't exact, but the result looked something like this:

    public isTheFooBarred(class Node { int[][] positions, int size } node, int x, int y, Set visited = new HashSet(node.size)) {
      // ...
    }

The first parameter to the method had an inlined class definition, and the last parameter was optional. We discussed this and the candidate claimed that this was legal vanilla Java. In the case of the last parameter, the candidate claimed that the compiler generated every possible combination of methods including and excluding each of the optional parameters (so, 2^n methods).

I really tried to give the candidate the benefit of the doubt, and asked if there was some sort of annotation processor or code pre-processor that they were using, but they were adamant that it was plain old vanilla Java. I'm pretty sure that they were using some in-house built thing, but their solution had significant problems, so it wasn't the only reason I was against the hire.