if anything changes I'll let you know
something you say after a lame excuse to cancel plans with friends, usually for a better offer, without any real intention of considering original plan
a guy you've been dying to go out with asks you to dinner Friday night:
Sorry Rachel - I won't be able to make it to your sister's middle school graduation Friday night - will need to work late that day but if anything changes I'll let you know.
Sorry Rachel - I won't be able to make it to your sister's middle school graduation Friday night - will need to work late that day but if anything changes I'll let you know.