C# In() method? (like Sql)

I'm having a hard time finding what, I think, should be a fairly simple method.

I think we've all used this:

select someThing from someTable where someColumn in('item1', 'item2')

In C#, I've have to write stuff like this:

if (someEnum == someEnum.Enum1 || someEnum == someEnum.Enum2 || 
  someEnum == someEnum.Enum3)
{
  this.DoSomething();
}

This works, but it's just wordy.

Out of frustration, I wrote an extension method to accomplish what I'm trying to do.

namespace System
{
    public static class SystemExtensions
    {
        public static bool In<T>(this T needle, params T[] haystack)
        {
            return haystack.Contains(needle);
        }
    }
}

Now, I can write shorter code:

if (someEnum.In(someEnum.Enum1, someEnum.Enum2, someEnum.Enum3))
  this.DoSomething();
if (someInt.In(CONSTANT1, CONSTANT2))
  this.DoSomethingElse();

It feels dirty, however, to write my own method for something that I just can't find in the framework.

Any help you folks can offer would be great, Thanks

EDIT: Thanks everyone for the in-depth anaylsis. I think I'll keep using my In() method.