using System;

using System.Text.RegularExpressions;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var findme = "hi";

        Regex re = new Regex($@"\b{Regex.Escape(findme)}\b", RegexOptions.IgnoreCase);

        List<string> data = new List<string>{"The child wanted to play in the mud", "Hi there", "Hector had a hip problem"};

        var filtered = data.Where(d => re.IsMatch(d));

        filtered.ToList().ForEach(Console.WriteLine);

    }

}