Do not accept terms and conditions

For mandatory T&Cs I'll put in the signature box "Decline", including updating the HTML page to say "decline" instead of "OK" and screenshotting it or modifying the HTTP response sent back to include riders.

I know it probably won't matter, but it's kind of fun for me.

No chance that would hold up in court. Clickwraps have been tested in courts and are fully enforceable.

And keep in mind that (at least in the US) the opposite of "I accept the terms and conditions" is not "I get to do whatever I want," it's "I am accessing this service without authorization, which is a crime under the Computer Fraud and Abuse Act."

Are you implying that if a US "service" consists of e.g. publicly accessible HTTP endpoints, it is illegal to use these endpoints in the US without "accepting" some terms and conditions that the provider of these endpoints requires its users to accept before using them?

I do not understand how such a requirement would be legally enforceable for public endpoints.