Cool? It depends on who it is that masturbated to you. Be careful what you wish for, they say.
It's one thing if an attractive guy or girl has lovingly caressed their genitals to the thought of you... but you wouldn't want to know if the creepy old man down your street or your own uncle has.
I personally didn't grow up imagining anyone alive would ever desire me in any way, so I didn't really think about whoever would masturbate to the thought of me, but... I wouldn't want to have this kind of knowledge either as I think that statistically I have more chances of being creeped the hell out (those sleazy old guys, old enough to be your dad or grandpa, who ogle teen girls, for example) than flattered.
A few years ago an online friend of mine has confessed having polished his pole to an innocent picture of me where my neckline just happened to be a little low, and I was... perturbated by the news. It would have been one thing if he had been someone I was attracted to, but he wasn't. I wasn't quite creeped out as he was younger than me and not otherwise creepy, but... just kinda not entirely okay with it, either. It's not something I would have wished to know.
On the other hand, my gf has told me, after I asked her, that she had imagined us having sex a lot of times, and I assume she has probably flicked the bean to the thought of me. And I found it hot, because it's her. It really depends on who it is, really.
But still, unless it's my own partner, I just prefer not to know.