My mom used to do all the cooking in our house. 
 
When my grandfather was ill and hospitalized for a month, my mom left the state to go help take care of him. 
 
I was living away from home, my sister and dad were home and apparently starting to get really tired of eating take out and frozen dinners.
 
My sister wanted a salad. My dad was down. A coworker at her salon had brought in an awesome salad for the Christmas Potluck and she had gotten the recipe and did my dad want to go to the grocery store with her, help her get all the ingredients, pay for said ingredients, then help her make the salad? 
 
My dad, desperate for some roughage and freshly prepared food was all for it. Disaster insued almost immediately. They made a list and headed to the grocery store. 
 
Everything seemed to be going ok until they got to the green onions. They looked everywhere and couldn't find green onions... and they needed eight of them. Annoyed and ready to head home they decided that white onions had to basically be the same thing... except that eight seemed like a whole ton of onions... and if you know the difference between green and white onions you would know that eight white onions is indeed a whole lot of onion for a salad whose main ingredient was not supposed to be onions.
 
But they decided, the recipe said eight... so eight it was.
 
They gathered the rest of the ingredients, dad paid, and they drove home to start the salad. They chopped up everything and when it finally came time for the onions, they double checked the recipe... yup eight onions... shrugged and began cutting... all. eight. huge. white onions.
 
By all accounts the house stunk and their eyes were watering something fierce when they finally managed to finish chopping the final onion. Per the recipe's instructions they added the eight chopped onions to the top of the salad and did their best to disperse them evenly.
 
They later laughed hysterically telling my incredulous mother and I that the layer of onions was at least three inches thick on the top of the salad and that they both got absolutely horrific heartburn from the few bites of the salad they were able to choke down.
 
A memorable way to learn the difference between green and white onions I reckon.