2 Asian youths enter a local Boots, picked up a can of deodorant the shop assistant asked one of them ( The clever one) to put the can down, he did not and began to spray onto his clothes! what would you do?
To fully answer the question TWR, in all seriousness I wouldn't do a thing. I might say something, but I wouldn't risk being assaulted which could so easily happen when you confront anyone.
Not sure why you feel the need to point out that they were Asian...
Anyway, why did the assistant ask them to put it down in the first place? Where they causing a nuisance before they started spraying? I would ask them to leave and if they didn't call security/police.