Next time some literary snob type tells you, in a world-weary sort of tone:
“ I suppose you don’t know what a synecdoche is,”
You can answer:
“Everybody knows that. Synecdoches form images in our minds with a convenient sort of shorthand. They help create our understanding of the entirety via a glimpse of only one part. So there.”

‘Synecdoche’ possibly isn’t one of your top 100 daily words.
(But if you want to haul it out at your next party make sure you pronounce it right.
Sort of like Schenectady)
Your synecdoche-comprehension is, however, perfect.
If I told you I got a ‘new set of wheels’ you wouldn’t congratulate me on a tire purchase.
You’d know I was talking about my (mythical) new car.
You celebrate with bubbly, sign your John Hancock, count heads and pay with plastic and you are a MASTER of the synecdoche.
‘All hands on deck’ demands more than just hands, but isn’t it so much more fun than asking all competent personnel to come topside? A Romeo and Juliet couple is headed no place good and if someone calls you Charlie Brown they don’t necessarily mean you are well-drawn.

Charlie Brown carries the burden of all lovable losers on his narrow shoulders. He can handle it. He’s made of ink, for goodness’ sake. A Venus is a synecdoche for lovely women while a Jane Eyre-type is plain but will get the blind bigamist in the end. It’s OK. The originals aren’t real. Elmer Fudd can be a stand-in for cartoon hapless hunters but don’t think for a moment he represents the whole of the real world of hunters.

With all that said, let’s check your synecdoche prowess.
‘Single mother’ What pops into your head?
How about ‘Homeschooler?’
‘Young black male?’
Is your brain ready to explode with the millions of different single moms, homeschoolers and young black men?
Are you shouting,
“Is that Tuesday Prude crazy? How can one single mom possibly stand for all single mothers? How can one homeschooled kid or young black male create our understanding of the whole?”
You know it isn’t possible.
Not everyone has your grasp of the obvious.
Some will take a hard-working single mother and use her to convince us that ‘single mother’ is synonymous for ‘hard-working.’
Someone whose identity has been stolen by a single mother will use her as a synecdoche for every single mother.
Kids schooled at home are kids. Some neatly dressed who call adults m’am or sir, some with Supreme Court-level comprehension of the Constitution, some playing video games all day in their pajamas. But there are folks out there—really, I have met them—who assume that the single homeschooler they’ve had access to must represent all those who are homeschooled.

Wisecracking Will Smith-type rascals, noble George Washington Carvers/Martin Luther King Jrs, or hardened African American gang members are incapable of helping us comprehend that entire elusive classification of ‘young black male.’
One single mom can’t represent all single moms. No woman can bear that burden. Since homeschooled kids are as varied as otherly-schooled youngsters it would be an impossible waste of energy to find one synecdoche for the whole.
Young black men, like young black women (or whatever hue or gender) face enough challenges. They barely know themselves. Heaven forbid one of them function as stand-in for everyone in their bracket.

Synecdoches make great figures of speech but lousy stereotypes.
Like literary device elitists, they must be kept firmly in their place.