South Park Muslims?

I'm still not sure how I feel about this (english language) joke that I found on an arabic site:

An old Arab has been living in New York for over 40 years. He'd like to plant his garden with potatoes but he's all alone, too old and weak. He emails his son who's studying in Paris:

Dear Ahmed, I'm very sad because I can't plant potatoes in my garden. If you were here you could have helped me turn over the ground. Love, Your Father.

The reply arrives the next day: Dear Father, whatever you do, please don't touch the garden! That's where I hid the thing. Love you too, Ahmed.

At 4 am the next morning the US Army, Marines, FBI, CIA and a SWAT team show up and comb every inch of the garden, then leave disappointed for the found nothing.

Another email from the son arrives later: Dear Father, I'm quite sure the garden has been turned over by now and that you can plant your potatoes. It was the best I could do. Love, Ahmed.

I mean, just a few days ago I railed against young muslims making light of American fears... But, on the other hand, it is a pretty funny joke. And if I consider myself a South Park Conservative, feeling free to make fun of current events, no matter how tragic, doesn't that make the author of this joke a South Park Muslim?

The big question... Is 9/11 safe for satire? I know it's been done... but is it socially acceptable?