If you insist, they could take me to court for not paying the bill, at which time they'd have to accept USD for the debt.

So yes, they could refuse the $100 and then sue me, at which point they'd have to take it. So you'd get a big clap for technically "winning" this argument but in possibly the dumbest way possible.

In practice, the reason why 'legal tender for all debts' is relevant is because it pretty much forces to take my $100 or go through an expensive process to just end up with the same result.