that you spend money you don't have and end up being overdrawn $100?

Why would someone say "The bank messed up my account and I am overdrawn $100."?
Because people must blame others for their failings instead of taking responsibility for their own screw-ups.
Good Question. People don't like to think that they are the ones at fault, so they like to blame someone else, and the big faceless bank is an easy target.

Now, with debit cards and electronic payments, it is much easier to make an error and cause yourself an overdraft than it ever used to be when a checking account only had checks. Unfortunately, a lot of people do not actually understand how their debit card works, why checks don't clear instantly, that using the debit card at places like a gas station puts holds on their account which means those funds are no longer available, etc and that causes a lot of these errors people make that cause them to become overdrawn. Ultimately, if one doesn't understand the debit card or electronic payment, etc it is their own responsibility to figure it out, but too many people are just too lazy, careless, irresponsible or whatever to be bothered to educate themselves about these matters. It's just easier to blame the bank.
People sometimes assume if they don't have money their debit cards will not work. Many banks will let their customers continue to use their debit cards (up to a certain limit). The person gets the convenience of spending and the bank makes money with overdraft charges.

I have seen a monthly service charge overdraw an account. The bank pays the customer's checks and debits but the overdraft charges can easily add up to $100.
That statement comes from the younger generation. They were the ones raised under the banner of Make them Feel Good. Schools and parents always told them "That's Okay, it wasn't your fault"
Then as adults that still sing that tune. The best was the one that said Car Loan Companies set you up to fail by making the loan payments to high to afford. Yeah right like someone twisted her arm to buy a 30k new car.
Because it is so much easier saying it's the bank's fault, or your mom's fault, or the other guy's fault, than looking yourself in the mirror, and realizing exactly whose fault it is.
It is just natural to try and blame someone other than yourself.

it is of course not the bank's fault.