using System;

using System.Linq;

using System.Collections.Generic;                   

​

public static class Program

{

    public static void Main()

    {

        var list = new List<long> { 1, 2, 3, 1, 1, 1, 2, 10};

        var exc = new List<long> { 1, 2, 3 };

        var result = list.ExceptUnique(exc);

        Console.WriteLine("Count = " + result.Count().ToString());

        Console.WriteLine();

        foreach(var item in result)

            Console.WriteLine(item);

    }

    private static IEnumerable<T> ExceptUnique<T>(this IEnumerable<T> source, IEnumerable<T> except) where T : struct

    {

        var exceptList = except.ToList();

        return source.Where(x => Compare(exceptList.PopFirstOrDefault(e => Compare(e, x)), default)).ToList();

    }

    private static T PopFirstOrDefault<T>(this IList<T> source, Func<T, bool> predicate) where T : struct

    {

        var item = source.FirstOrDefault(predicate);

        if (!Compare(item, default))

        {

            source.Remove(item);

        }

        return item;

    }

    private static bool Compare<T>(T x, T y) where T : struct

    {

        return EqualityComparer<T>.Default.Equals(x, y);

    }

}