What are some good pranks to play on my ex-friend?

Well the other day me and my bestie were at the mall and we got on the escalator to go back downstairs and she just pushed me like really hard and i fell down and broke my leg. When she got down to the bottom where i was, she poured her frappe all over me and walked away with a group of girls and began giggling. So any revenge ideas? Don't hold back! Think of the worst thing you can and then make that worse! We were friends for five years and i don't know what her problem is.