First, if the manufacturer bothers to include something on the label that says, "do not apply to broken skin," they really mean it.
Second, if you must indulge in compulsive triceps-firming dips (we'll avoid shredding your fantasy that they'll magically firm your upper arms within the next 15 minutes), try not to use a rolling chair.
Both of these things are stupid, and will hurt right away. Moron.