First time I flew on a 747 we landed at Boston and it was +90F outside and the air conditioning fogged.
As usual, when the unexpected happens, some of the pax looked concerned, some screamed and some even did not believe the cabin crew announcement and continued to panic.
On another trip I boarded a BAe 146-100 at Glasgow and sat down.
Within a couple of minutes I could have been sitting on top of a Scottish mountain in cloud.
The crew stopped boarding and put out an announcement that we should disembark ...using the seat backs as a guide as the floor strip lights weren't visible unless we were to crawl. When we got off, I got to worrying about the intensity of the floor lights.
Eventually they cleared the fog but after take off it came back, though not as thick, and remained with us, sometimes in great clouds, other times just a trace, all the way to Gatwick.