Bad things about your favourite programming language

Last time I checked, Java knows not about unsigned primitives. It was a total shocker to everyone when I asked "how to unsign long?"

BigInteger, a very slow implementation that handles any amount of huge digit

Code:

long val = 123456789;
BigInteger uLong = new BigInteger(String.valueOf(val & 0xfffffffffffffff));

Something that I'm very annoyed with when dealing with conversion of code between C/C++ to Java such as Nexon's Randomizer.

Problems with C# (version 4) in general:

- Compiles to MSIL, no (feasible) way to compile to x86. You either use commercial products to compile everything your application depends on to x86, or you live with MSIL (and JIT). There is also AOT but that is merely for improving performance, not for running applications on platforms without .NET.
- .. nothing with the language ...

Problems with the .NET Framework in general:

- Cross-platform interoperability - it took Microsoft years to develop. Now the open source community has to match that, if they want it on linux and Mac. PITA, much?
- It is huge. But Vista/7 now come with .NET Framework 3.5 so that isn't much of a problem.
- Too easy to reverse engineer - suppose this is a problem with all intermediate languages

Other than that, I love C#.

Not really, C# can be difficult to be reverse engineer with the correct tool.
Till now I've yet to see any good proxy API based obfuscation on Java and C#, which I've been working on it at around January 2010. With that, all the APIs from Sun/Microsoft can be obfuscated and renamed to our own custom one and compiled into the executable. That will create a whole chunk of garbage that cannot be understood by people.

I guess you've tried decompiling CSharp's client?