So.........reading between the line, it sounds like you may be saying your loved one who has Dementia/Alzheimer's stands up during a meal and pulls his/her pants down? Is that it? There is no rationale to this brain disease; nothing makes sense. You can purchase an Alzheimer's jumpsuit online (Amazon.com) that zips up in back and prevents a person from undressing himself or removing an adult incontinence brief while awake or during sleep. These garments are particularly useful for those who prefer to be naked!
https://www.amazon.com/Talit-Inc-Womens-Alzheimers-Clothing/dp/B07KPPLZM6/ref=sr_1_1?crid=1Y74RA6682XK7&dchild=1&keywords=alzheimers+jumpsuit+with+back+zipper+womens&qid=1578967522&sprefix=alzheimers+jumpsui%2Caps%2C176&sr=8-1
Best of luck!
Gotta learn to laugh at the truly absurd things that they do.
-Abraham Lincoln