Mine

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Text;
using System.Net;

namespace Server
{
    public sealed class ClientDetailsCollection : KeyedCollection<IPEndPoint, ClientDetails>
    {
        public ClientDetailsCollection()
        {
        }

        protected override IPEndPoint GetKeyForItem(ClientDetails item)
        {
            foreach (KeyValuePair<IPEndPoint, ClientDetails> kv in this.Dictionary)
            {
                if (kv.Value == item)
                {
                    return kv.Key;
                }
            }
        }
    }
}