I've been trying to figure out what it was about this that bugged me and (finally) looking at the link made me realize what it is. It's the varied interpretations that are bound to come out of this. If you look at the first two pictures, I see everyone in the "wear this" example wearing black & white, maybe some gray and a bit of khaki. And the people in the "not this" picture wearing pretty colors.
I didn't even notice the tie thing until I reread turnip's post. So for me, it wasn't about the specific dressiness of the clothes they are wearing, but the colors.
What I'm trying to say is that everyone who looks at these pictures has the potential to interpret them differently. For me, it says, wear neutral colors only to the cookout. Don't dare show up in any colors. That's not really what they mean, is it?
I think that if I were invited to a cookout I could go in my closet and figure out the appropriate clothing. Or if they said, "Casual and Comfortable" for the wedding, I'd get that. Or if it's an unusual venue, like the Buddhist hall, a little extra description might be in order.
But I think showing one picture of "do" and one of "don't" doesn't do it for me. I did read the descriptions below the pictures, but they didn't really help. As turnip points, out there's a guy wearing a tie in the "do" picture but the caption says, "bathing suit, shorts and flip flops", which pretty much no one in that picture is wearing. The caption for the "don't" picture references The Housewives of Orange County, which I've never seen and have no idea how they dress, save all those lively colors in the picture!