I know what to do... so why don't I think of it until it's too late?

TiFU. I'm 47yo... I should be able to say "I don't give my number out, sorry". My absolute bff is left on read in messenger since 2 days ago. I have zero interest or energy in communicating with a random customer outside of the pleasant small talk I was being paid for when he asked for my number. It caught me off guard... aren't we old enough to KNOW not to put trapped workers AT THEIR JOB on the spot with uncomfortable and inappropriate personal requests??? Fml... where was my usual lightning quick sassy decline??? UGH. Why is this shit still a thing?