@sillyyak52, If it makes you feel any better, I have a sibling who thinks the dinner table (at fine dining restaurants, and less formal pub grub settings etc.) is a personal buffet table and dips into the food of whoever is sitting beside or opposite to them just to get a taste (no plate is safe!) ... never asks for permission ... and has no consideration of gluten cross contamination even though I've explained it diplomatically with articles, pictures of dermatitis herpetiformis (which I've had for years) like @knitty kitty and I both suggest you do. I avoid that sibling at restaurants now and sit at the opposite end of the table out of arms reach! I've had similar treatment at a recent siblings 60th BBQ with family and friends (brought my own food and burger), where I was told (in a very rude manner) "tough luck, there's nowhere safe ... just cook your burger on the BBQ" which was cross contaminated ... I stood my ground and asked for a clean frying pan to cook my burger safely and separately. 

knitty kitty makes a good point. Avocados are high in histamines. So are bananas. Both also trigger histamine production in the body when consumed so there's a double whammy with those two foods for those struggling with histamine intolerance/MCAS

@Sharke, The updated guidelines for a gluten challenge are to eat ten grams of gluten per day for two weeks minimum.  Lesser amounts of gluten (3 grams) don't provoke an immune response strong enough that the antibodies leave the gastrointestinal tract and get into the blood where they can be measured in tTg blood tests.   Have no doubt that the antibodies made in the small intestine are doing damage there, even if you don't suffer severe symptoms, yet. Did you react to barley prior to going gluten free? Have you been checked for chronic autoimmune gastritis which is another autoimmune disease that sometimes occurs with Celiac Disease? Have you been checked for nutritional deficiencies?  Thiamine deficiency (Gastrointestinal Beriberi) can cause constipation and/or diarrhea, abdominal pain, and weight loss.   Thiamine Deficiency Disorders https://pmc.ncbi.nlm.nih.gov/articles/PMC8451766/  

@sillyyak52, Count another one in the same boat!  My family has always been in denial.  They said my tummy aches were a ploy to miss school.  My parents passed from health problems associated with uncontrolled Celiac Disease (Abdominal Aortic Aneurysm and Glioblastoma brain tumor).  My sister still has her head buried in the sand.   I agree with @Rogol72, try the consequences of untreated celiac disease shock treatment.  Sometimes people are just scared of having to change their comfortable lifestyle.