when the scrotum is relaxed ... & ...even more pleasurable if you get your wife
Tried above but unable to stay relaxed.
Seriously, I think that some men will have a problem with this. They don't see it as the 'done thing'. Others will see it as questioning their 'manhood' or think that they have too much testosterone for it to happen to them.
My brother in law was told by his wife that 'something was different' one night. A trip to the Doctor, Hospital etc. Result - one testicle removed.
At the time he was 23 years old and otherwise as fit as a fiddle. It was a sharp lesson to the rest of the men in the family.