There are definitely references to um... "adult activities" throughout the Hitchhiker series, and I remember being surprised that there was an entire chapter explicitly devoted to such activities. I think it was in So Long and Thanks for All the Fish (book 4) when Arthur met up with Fenchurch, but it's been a long time since I read the series.
https://en.wikipedia.org/wiki/So_Lon...r_All_the_Fish