Join with And

join.cs

public static string Join<TItem>(IEnumerable<TItem> items, string separator = ", ", string end = " and ")
{
    var builder = new StringBuilder();
    using (var enumerator = items.GetEnumerator())
    {
        if (enumerator.MoveNext())
        {
            var item = enumerator.Current;
            if (enumerator.MoveNext())
            {
                builder.Append(item);
                item = enumerator.Current;
                while (enumerator.MoveNext())
                {
                    builder.Append(separator);
                    builder.Append(item);
                    item = enumerator.Current;
                }
                builder.Append(end);
            }
            builder.Append(item);
        }
    }
    return builder.ToString();
}