So the scrotum is supposed to contract in various situations - when you're about to come, when you are about to be eaten by a tiger and need to get away as quickly as possible, and when it is cold so that the hermunculi in your balls don't decide to hibernate and end the species (it's actually the other way around - our bodies push the balls away when it is too hot). I have generally found that I have no balls after a good bout of swimming, and pretty much any time I have a job interview. Stress makes my balls suck in in many situations. I think my body is telling me "dude, we're not going to need the man-juice, and I'm leaving the energy to your big head not your little one". My balls override my brain's decision on this point.
So I think answering the OP - I don't think it is strange that my balls have a mind of their own (I lived through puberty), I also don't find it surprising that different ball-brains would have different views on when to suck in and when to suggest to their net door neighbour to bone up.
It sounds like yours (OP) think every visitor is a potential ejaculatory opportunity, and they want to be ready to go. You need to take them aside like a 13-year old son or nephew and explain to them that you understand that they are going to have special feelings, but that they need to learn to control their feelings if they are getting in the way of polite society.
My balls say "good luck with that".
Matthew