You can't polish a turd.

That is very good advice, both metaphorically and literally, you absolutely cannot.

That old adage. It's not what you know, but who you know. Possibly all that more relevant in today's society.

I'll always remember my father saying "Never trust anyone who doesn't like animals". It's served me well so far.

but you can roll it in glitter

I have seen one dried, varnished and mounted on a plaque.

"There is no worse sight than watching ignorance in action"

QED these and similar forums, but RL fans is a strong contender for poll position, with several outstanding contributors.

Never put your fingers where you wouldn't put your penis.

Never play backgammon with a Greek or arm wrestle them.

So you'd happily put your penis in a tube of Pringles?

When I was 15 I did my school work experience at an Architecture firm, there was an old character called Will who was a typical old bloke of the office whom offered a lot of experience and wisdom to the younger Architects and technicians. One day we got on to the subject of under aged drinking and after much discussion about the evils of alcohol he turned to me and said;

"everything in life is good in moderation, except sex, do that as much as you can"

Probably the best advice I've ever had.