I've had this and solved it. For me it was the button on my jeans.
So I now:
wear a belt and turn it inside out, so the buckle front, with the pin, is against the jeans button, not the inside of my t-shirt, if that makes sense
I've made a big effort not to lean against counter tops when baking etc, because I think this is the main problem with me
I've bought fabric stretchy belts with fasteners and made sure the fabric is over my jeans button and the fastener/buckle is off to the side (NB I never tuck in) The belts I have don't have big buckles that stick out like a leather belt buckle does, under a top
I have started buying trousers that do up at the side or are just pull up/elasticated at the waist, or drawstring
I've tried putting a square of material over the button, ie before I do it up, but I don't know if that's helped as the above seems to have sorted it for now
People who tuck in do not have these problems, I betcha.