Well, I thought it was funny...

[Roger Kettle]

On my desk, I have a New Yorker Cartoon Calendar, one of those tear-off jobs with a different gag every day. It's an annual and welcome gift from my niece, Eilidh. Yesterday's offering showed two typical, rich American ladies sitting in an expensive restaurant. One of them is saying...
"I've only been gluten-free for a week, but I'm already really annoying."
I laughed, I did.

[Diane CBPFC]

 

[Mince]

Those with Celiac disease have to avoid gluten, as do those who are allergic to gluten. It would be interesting to see if the gag would work the same if it was lactose-free of those lactose intolerant, or nut-free for those with nut allergies.

Perhaps the gag works on the reader's assumption that being gluten free is a choice, and an annoying one, rather than a necessity. I wonder if those who are gluten-free laugh at cartoons of those who say, 'I've gone back to eating processed food, and I'm feeling dumber already.'

[Roger Kettle]

Works for me!
The gag is a piss-take of the many people who jump on dietary trends without medical reasons---those who do it simply because it's fashionable. It's certainly not about genuine sufferers of Celiac disease or similar ailments. That wouldn't work. 

[Mince]

I have to admit that I had not seen it that way, in which case it's fine.

How about homeopathy? Many take homeopathic treatments for ailments, even though all evidence points to it being useless. Is that open to humour. (My answer is yes - if you're that stupid, you probably would not even realise you're being lambasted anyway.) But for things like veganism (ethical reasons) or plant-based diet (health reasons), perhaps I would find the humour ironically odd. It's interesting.