Funny you should mention that you get a boner after running.
There's this guy I see out running most mornings and he looks pretty fit. About 40 but in good shape. Always wears a short T-shirt top and tight silky running shorts with a slit up the side to stop leg chafing. I've watched him for ages as his junk wobbles from side to side as he runs, shorts have a cock bag in them I guess so that nothing falls out.
The last few mornings our paths have crossed and we've taken up to chatting while he does a few stretches - though often as not he's just waiting to chat, have a breather. Not that my eyes were glued to his groin but I was very aware he was getting a boner, I could see it growing to the side and it was taking up space in his shorts - this morning he had to adjust himself, he smiled as he did it, saying "it happens". Needless to say I was pretty chubbed as well with the show and I know he saw it. The thing is do I make a point of noticing next time in case he'd like to take it further, I'm getting the vibe just not the action.