Did your friend play any contact sports like soccer? CTE can cause these things.

i find it hard to believe it's a thyroid thing.

I had a TT and TC and thus am kept very suppressed (hyperthyroid) and i dont behave like this.

My mother was like this while still passing dementia screen. She had always been like this before, just milder, much milder and could hide it from others. It took a long time to finally detect dementia. I think a few years after this decline and her being on psychiatric meds they went to mild cognitive impairment, but she also was lying to me a lot and paranoid and no longer let me know medical info, so it may have been dementia.