How to send an email to nine thousand, five hundred and forty-two people:
Put every one of the 9,542 email addresses in the To header. Send email.
Piss off any of those 9,542 people who are using Outlook Express, as Outlook Express wedges solid with 100% CPU usage when given 200kB of To header to parse. Annoy any of those 9,542 people who are using Thunderbird, as Thunderbird's renderer does strange things when given 200kB of To header to parse. Annoy any of those 9,542 people using Pine, as Pine crashes when commanded to show full headers of an email with 200kB of header.
And piss off the administrators, who have just had nearly 2 gigabytes of email pass through their servers.
Nice one, Student Union Comms Officer.
Irritatingly, this doesn't seem to actually violate RFC 2822 as long as the lines are no longer than 998 characters. Grrr.