Hey love,
these Czech "ahoj" and "čau" are pretty stupid. I don't know how both words can mean both "hello" and "bye-bye" at the same time. That's why I got confused a lot in the first few years.
Once it happened that I was going home and again thinking deeply about something (in Russian of course). I met a colleague and didn't have time to switch quickly. I had to quickly choose between ahoj and čau. You know what I finally used? Ahoj? Čau?
Tea, dude.