It is about 15 years ago now but I had to call my ISP for something. Part of the support guys scrips was to ask me if I had an apple or windows machine. I responded that it was a Linux box. To which he told me he wasn't sure if "their" Internet was compatible with Linux.
I recently moved to a fairly rural area in the midst of them setting up fiber throughout the area. For some reason, the ISP is something like halfway across the country from me. I asked them to setup port forwarding; the first few tech support people I talked to didn't even know what that is. Eventually they relayed the question to an engineer who was familiar with the concept but still had a lot of irrelevant questions, many of which were about the operating system I used. It was ... Frustrating.
I did finally get port forwarding, but it took literally a month and a half, figuratively a million calls, and ten to twenty of their staff over at least three departments. I'm happy now, though.
Edit: sorry about the initially irrelevant and probably boring post. I accidentally pressed post prematurely.