JavaScript itself would be fine as long as browsers didn't present certain capabilities to the running script. Modifying the DOM and rearranging elements? Go ham. Intercepting input and hard-forcing viewport sizes? Fuck outta here.

Edit: I've been getting the "slow down" thing on HN for the last couple of weeks after like five or six messages within a half hour. Not connected to HN through any VPN or obfuscation. It's annoying because it seems to take a solid hour or two (haven't measured) to unlock.