At some point, I intend to set up two gmail accounts just temporarily. These accounts will each be set to forward to each other. Then, as soon as one of the accounts gets a single email, the email will be sent back and forth until there are thousands of copies in each inbox! Eventually, something will happen to stop this, but until it does, it'll look pretty cool. The process could be escalated by turning on not only normal forwarding, but filter-based forwarding and POP-3/IMAP, as well as sending multiple messages.
I'll post the results here when I do it.