"Liquor before beer, never fear. Beer before liquor, never sicker."
"Red sky at night, sailor's delight. Red sky at morning, sailor's warning."
"Leaves of three, let them be."
Helpful warnings, couched in rhyme. Judging by the search results on Google, that first one is confusing to many people, and an urban legend to boot.
But what about sayings that are relevant to life today? We are not sailors, except on the tides of social media. We do not encounter poison ivy, because we never go outside except to get in our cars to drive somewhere and go inside again. Where are the rhymes for our times?
I've taken it upon myself to come up with some that I hope will catch on like (virtual) wildfire.
First and foremost: "Meet them online, everything's fine. Meet them in person, things may worsen." This, coupled with "Make it funny, you're in the money; if it's lame, you're to blame" should just about cover any social situation you might find yourself in.
More general advice for modern living:
"Aiming for nonagenarian? Go vegetarian!"
"Red as a beet? Don't eat that meat!"
"If it has lime, it's worth your time." (Electric Company, anyone? Anyone?)
"If the zombies are walkin', don't go a-knockin'"
"If he's flashing fang, don't tap that thang."
"Leaves of seventy-one, isn't counting fun?"
"Cat on the lap, prepare to nap. Cat on the floor, OK to adore. Cat on the 'nip, prepare for a trip."
Given five or ten years, I'm pretty sure that these too will be myths that NBC Today Health will be happy to debunk for us.
Additional cautionary sayings encouraged in the comments.
ETA: "Neither a borrower nor a lender be, unless you work at a library."