Big Al's won't care? Hmm, that's strange, because most if not all of the Big Al's here in Canada are pretty protective of their stock (at least the ones I have been in.) But I guess it varies from store to store. Their store in Florida is their only one in the US. I guess it depends on the poeple. Now back on subject...
You did nothing wrong by telling him he is not welcome. what you should have done is convince him that a Peacock mantis shrimp (the largest one, preferably) is a cleaner shrimp. You could get a kick out of THAT one. I actually did it to my friend once after he'd done something stupid as revenge. It was only a small G. Ternatensis though.