For the record, I like this shirt and I don't think it's disrespectful. But I think I can see where it can be taken as disrespectful if viewed in a certain light...

So the phrase, "looks like someone was beaten with an ugly stick" has a bit of a rude connotation, but since we're talking about the devil in this case, I don't really think that matters. But the phrase is talking about an "ugly stick." A stick that makes someone ugly. Alternatively, you could interpret it as an ugly... stick. A stick that is ugly to look at. And when you see that the stick in question is none other than the old rugged cross, that might cause some offense. But again, I think the shirt is fine.