you mean how to say "You could have at least said bye" in Turkish? Well you can say "En azından bir hoşçakal diyebilirdin." Here, bye means "hoşçakal" but you can use "güle güle" or "bay bay" too. I hope it will help :) edit: i've read it as there was "at least" it doesn't change, in fact.

u can use for "bye" =güle güle or hoşçakal, so you could have at least said bye=En azından hoşçakal diyebilirdin,