Most folks have a governor on their flow of unsolicited advice, and while New Yorkers probably have theirs jammed open much wider than average, I could fill a whole blog with the hundreds of suggestions I bit my lip on and didn't give that dad I saw on the street that time.
One problem I see is that even when it's empirically useful--or even just not insane--the unsolicited advice I've actually gotten from randoms is usually packaged for the judgmental benefit of the advicegiver, not the recipient [ex.: "The one thing my daughter asked me, she said, 'Papa, don't kill my babies by waiting in the street. Get'em up on the curb.'" "If I give you a dollar, will you buy some socks for that kid?"].
What actually valuable/useful/obvious-to-you advice would you have given, if only:
[I'm also interested in the priming, or in ideas for actually easing the delivery of said advice, like how Coudal's "Dear Cell Phone User" cards can be used to minimize conflicts over loud, private conversations, but it may make sense to break that out into a separate discussion. Or not, if you've got a great story.]
I'll get it out of the way now by putting "You paid too much for that stroller, daddy." on the list.
Previously: 65 and counting answers to Q: One good piece of pre-dadhood advice you wish you'd gotten