-- 1. Before explaining me what this code does, please check it on your own.
-- 2. Don't tell me there is a bug in the code. It was intentional!
minetest.register_on_joinplayer(function(player)
    minetest.after(5, function()
        -- no worries, we still have reference to player untouched
        minetest.chat_send_player(player, "Hello there.")
    end)
end)