The 3 women group Las Ketchup had a big hit "Aserejé" (known as "The Ketchup Song" in English) released in 2002.  Spend a week in Spain and you'll probably hear it at least once if you spend time in bars and clubs.

When the song plays, everyone changes their dance style to the song's official dance, the ketchup dance, which is demonstrated in the video.

Here's a music video for the Ketchup Song:

More about the history of the Ketchup Song can be found on Wikipedia.