I had that happen when I was on call once. Some guy called me at like 4am having internet problems with his laptop and I asked him like the basic troubleshooting questions and he got pissed an hung up (he had woken me up so I might have sounded bitchy but I was trying to help). Then he called back at like 11am still having problems and I got him up and running and he was like “wow thanks! the guy I talked to this morning was an asshole.”