San Francisco's annual Valentine's Day Pillow Fight will once again muck up Justin Herman Plaza at 6 p.m. sharp tonight. And, no, they will not provide you a pillow; you need to bring your own. You also need to play nice. Here are some of the rules, which include the new suggestion of wearing a mask:

Mask is important. Cover your nose so you can breathe. Either a bandana or painters mask. You won't need it till towards the end, once the pillows are splitting. You'll need it even less if people are smart and get cheap synthetic ones that last longer and don't spew down.

Also, if you can, bring a trash bag with you to help clean up at the end. It gets messy and ends up costing the city loads of money. But, as SF Appeal points out, "city workers will be ready for the post-fight cleanup."