To get rid of your mehndi / henna design fast, wash the area often, with strong soap and a scrub brush. You can also use an exfoliating cream or something with alpha-hydroxy. If you are very desperate to get rid of your design, you can scrub with a weak solution of bleach and water. You must be careful with the last method, because this will take the design off right away, but it might also take your skin off. Use of lots of lotion is recommended.