In Chandler, Arizona, there is annually held a Cinco de Mayo chihuahua race for big trophies and tons of goods from various pet supply companies. The chihuahuas must be pure bred, vaccinated, and on leashes when not racing.
There's a separate King and Queen competition for chihuahua costumes, some of which are shown above and below.
There are similar chihuahua races in several cities, some of them likewise for Cinco de Mayo (as in Shreveport, Louisiana; Longmont, Colorado; Phoenix, Arizona; etc), plus others at other times of the year.
The annual Cinco de Mayo celebration is "to honor the Hispanic community's many contributions to the City of Chandler." Besides the hugely loved chihuahua races, there are authentic folk dances, music, a health fair, Mexican food, classic car show, and crafts.
For 2010, the winners of the King and Queen competition were Princess, now Queen Princess, held in the photo below by young Linda Moon; and Freddie, now King Freddie, held by Debra Arthur. I wish my town did cool stuff like this!