public static IEnumerable<T> Distinct<T, TKey>(this IEnumerable<T> items, Func<T, TKey> keySelector, IEqualityComparer<TKey> comparer)
{
    return items.Distinct(new KeyEqualityComparer<T, TKey>(keySelector, comparer.Equals));
}

class KeyEqualityComparer<T, TResult>: IEqualityComparer<T>
{
    private readonly Func<T, TResult> _KeySelector;
    private readonly Func<TResult, TResult, bool> _Predicate;

    public KeyEqualityComparer(Func<T, TResult> keySelector, Func<TResult, TResult, bool> predicate)
    {
        if (keySelector == null)
            throw new ArgumentNullException("keySelector");
        _KeySelector = keySelector;
        _Predicate = predicate ?? System.Collections.Generic.EqualityComparer<TResult>.Default.Equals;
    }

    public bool Equals(T x, T y)
    {
        return _Predicate(_KeySelector(x), _KeySelector(y));
    }

    public int GetHashCode(T obj)
    {
        // Always return the same value to force the call to IEqualityComparer<T>.Equals
        return 0;
    }
}

// TODO: Use C# 6 primary constructor and read-only autoprops :)
public class Person
{
    public string Name { get; set; }
    public string Hobby { get; set; }
    public string Profession { get; set; }
}

var people = new List<Person>
{
    new Person { Name="Tom", Hobby="Minecraft", Profession = "Student" },
    new Person { Name="Robin", Hobby="Taunting", Profession = "Outlaw" },
    new Person { Name="Robin", Hobby="Angry Birds", Profession = "Student" },
};