How do I make some nasty mud?

This Saturday the high school I graduated from for their FFA is having a car wash and I want to take my car there to get it washed but it hasn't rained in a while to take it out normally and get it mud to. I just want to make my own. I know how to make mid but is there a way I can make it especially annoying. They all know me as the guy who's probably gonna show up with my car especially dirty for them. So if there's a way to. Make it especially annoying its be helpful. Thanks.