Let's be real here, ordering anything from a fast food restaurant usually isn't healthy (even if it says it is). Logically, everyone knows that fast food isn't nutritionally good and should mostly be avoided because of that, but it's not always bad because of the calorie count.
Sometimes fast food items are bad because of the way they're handled or kept either before or after being made. A thread on Reddit focused specifically on this. The workers specifically talked about what exactly a customer should never order from their restaurant. Either because of gross practices, never-cleaned machines, bad ingredients, or just general unhealthiness, most places always have at least one thing that a customer should never order.
Warning: this will alter views on the globe's popular fast food chains. Be prepared to be grossed out.
These aren't super popular. That's not too much of a surprise. McDonald's is a burger fast food place. They aren't particularly known for their quality fish. So, if you truly expect anything other than the burgers to truly be fresh, then prepare to be disappointed. Filet-o-Fish is best avoided.
"When I worked at McDonald's the filet of fish was never ordered. We had to make them at 11 when lunch started and had the same ones in the tray until the elderly people came to get their supper at 3 P.M. Then replace them and we threw away those same ones when we closed. Never order them."