So, when you first meet Tinker Tom he offers to inject you with a chemical to purge your body of the microscopic bugs that the Institute is using to spy on you. The Doc mentions something about it containing battery acid, and when you ask about the contents, Tom DOES sort of mutter something like, "... and maybe a little battery acid...."

Did you take the serum? I did. After a fade-to-black moment, I came back with barely any heath left. Popped some stimpaks and went about my business. Was that just a ha-ha-ha, Tom is crazy kind of moment or did it have any real effect, I wonder? Tom's not ~entirely~ crazy, after all, and has developed some neat things.

Just wondering if anything happens if you ~don't~ accept his potion.

It doesn't have any long term effect. Deacon will "like" it if he's there when you take it, but most of your other companions will dislike it.

Would be cool if it actually did something. Even small, like 5% damage resistance to Synths or something.

Would be sweet if it did that, Tinker Toms coocoo, but the good kind of coocoo

It has battery acid in it, it almost kills you but it would kill any microscopic robots in your bloodstream.

I suggest sleeping in a bed right after that to not waste stimpacks

Wish there was a way we could call him out on it. Something like, “You idiot, that nearly killed me! Are you trying to deplete Railroad resources with your insane schemes?!”

That WAS an option, wasn't it? The #3 (right arrow) negative/hostile/no reaction? I usually pick the conciliatory / nice / informative options but it seems like that kind of response was available.

Yeah. There is an option to scream at him that it nearly killed you.