Or if you think you are posh

you just say TTFN!

for those of you not posh enough to know what posh means: story has it that it stands for Port out, starboard, home. This was supposedly printed on tickets of passengers on P&O (Peninsula and Orient) passenger vessels that travelled between UK and India in the days of the Raj. Britain and India are both in the northern hemisphere so the port (left-hand side) berths were mostly in the shade when travelling out (easterly) and the starboard ones when coming back. So the best and most expensive berths were POSH, hence the term.

TTFN