I have 2 bitches in season at the moment, and Jack, even though he's constantly whinging for the bitches(he has been used at stud),
he has never attempted to take his frustration out on anyone or anything else
He his 10 yrs old now, and if my memory serves me right, he did try humping legs when he was younger,but was always told a firm NO,and put in his crate!
The kids,who are all grown up now,and left home, used to find it funny,and sometimes he would be encouraged to hump,so I suppose the poor dog was slightly confused at the time .
Some brilliant posts on this thread BTW