Advised not to take acetaminophen or ibuprofen beforehand, to ward off possible side effects from the Covid shot, but what about aspirin?

i would ask your doctor about it

Don't take any of those before you take the vaccine. Aspirin is also used as a minor blood thinner given as an adjunct to stronger blood thinners to people that need that kind of treatment. Tylenol and Advil have a certain amount of the same properties. Your arm will get achy after you get the vaccine and you may have muscle aches as well. You can take any of those when your arm and or body has aches. The pain and fever medication you can get over the counter is Advil. It's better than the others

Who spread that nonsense?

Worked in health care for over 40 years and neve heard anything so ridiculous 

I heard that too, but it's ridiculous. I've got chronic pain and bad allergies. I've had anaphylactic reactions before and trust me, no amount of ibuprofen is going to mask that! Maybe for people who don't know their body or symptoms, but I damned sure won't be skipping my aspirin.

The idea is not to take any kind of a pain killing medicine so that you will know before it's too late if you're having a bad reaction if you take aspirin or some other painkiller it will reduce the feeling from any side effects.

You need to be on guard and not reduce the feeling from any side effects so that if you get something bad happening you can get to the doctor and get some kind of either a steroid or epinephrine.

so skip it for a day . 

Tylenol is ok, they even gave us it at the vaccination  hospital site. But the ANTI INFLAMMATORIES, such as ibuprofen and aspirin and a leave can mute the immune response to any vaccine and that’s why they aren’t to be taken