If actual an scientific white paper from PubMed with research and data does not convince you that coffee has a strong laxative effect on around 30% of people, then there's not much else to say.
There's still people who believe the world is flat despite all evidence to the contrary.
It's very difficult to have a discussion with someone who prefers their own opinions over science.
It's very difficult to have a discussion with someone who prefers their own opinions over science.