Anyone want my Portal 2 75% off coupon?

So, correct me if I'm wrong and this isn't allowed. I won Portal 2 on here (and was ecstatic) and with the game came a Portal 75% off coupon good until the 30th of August. Since I now already have the game and don't have money to buy another copy of the game and give THAT away, is there anyone that would like my coupon? (If this is allowed, anyways)

If so, please, comment here and I can add you on steam and I can trade it over. Not asking anything in return. I just want someone else to be able to use this and not have it go to waste.