Here's one I've seen used exactly twice in ten years - telephone validation. Imagine you annoy someone by spamming them and than have the destination site validate your data by phone, give it half an hour till a keyboard macro is setup that calls the chief of police or some knowledgeable technicians at the local telecoms company or when you get bored the originators of the spam (which'll kill the exploit pretty fast). And even better allow it to cycle with no delay line (say every two seconds) that'll not be used again for a while. The last idiots to try this were the buy your home fast for cash scammers over at Sellersaide.com and the current prize winners are currently hunched over with their 4000% plus payday loans at txtloan.co.uk, good one!
Ruffian antics are a wrench in society's gears