One of the most common places guys begin jacking off is while taking a shower. Many a parent has lamented their son(s) spend too much time taking showers, using up all the hot water. As young guys still living at home it's a favorite place because we think we're doing the deed "undercover."
Another Urban Dictionary definition I found interesting:
Beat it 'til it's cold: To masturbate in the shower until the water runs cold.
Well, I believe most parents know full well what their sons are doing - at least Dad does.
It's just not discussed. Though, their sons would be much more comfortable kicking back on their beds
if only parents gave them explicit permission to engage in such a normal activity without having to hide
And parents would save on power and water bills!