ExitCompare.cs

using System;
using System.Threading;
using System.Windows.Forms;

namespace Sandbox
{
    public class ExitCompare : Form
    {
        Thread BackgroundThread = null;

        public ExitCompare()
        {
            SuspendLayout();

            var table = new TableLayoutPanel { Dock = DockStyle.Fill, RowCount = 3, ColumnCount = 1 };
            table.RowStyles.Add(new RowStyle(SizeType.Percent, 33.33f));
            table.RowStyles.Add(new RowStyle(SizeType.Percent, 33.33f));
            table.RowStyles.Add(new RowStyle(SizeType.Percent, 33.33f));
            Controls.Add(table);

            var startThreadButton = new Button
            {
                Dock = DockStyle.Fill,
                TabIndex = 0,
                Text = "Start background thread"
            };
            startThreadButton.Click += StartThread;
            table.Controls.Add(startThreadButton, 0, 0);

            var applicationExitButton = new Button
            {
                Dock = DockStyle.Fill,
                TabIndex = 1,
                Text = "Application.Exit"
            };
            applicationExitButton.Click += (sender, e) => Application.Exit();
            table.Controls.Add(applicationExitButton, 0, 1);

            var environmentExitButton = new Button
            {
                Dock = DockStyle.Fill,
                TabIndex = 2,
                Text = "Environment.Exit"
            };
            environmentExitButton.Click += (sender, e) => Environment.Exit(0);
            table.Controls.Add(environmentExitButton, 0, 2);

            this.Text = "Exit Comparison";
            this.ResumeLayout(false);
        }

        private void StartThread(object sender, EventArgs e)
        {
            if (BackgroundThread == null)
            {
                BackgroundThread = new Thread(new ThreadStart(() =>
                {
                    while (true)
                    {
                        Thread.Sleep(1000);
                        Console.WriteLine("Background thread running.");
                    }
                }));
                BackgroundThread.Start();
            }

            ((Button)sender).Enabled = false;
        }

        [STAThread]
        public static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new ExitCompare());
        }
    }
}