You can't unless the admins specifically remove them... you will have to contact an admin @RedRain and tell her why you want the question to be removed... but I think they will only remove it when it is against the GaG guidelines
Hi! Actually you can't delete your questions but you can disavow them after 24 hs of being posted. That means the question will remain on the site as anonimous, but you'll no longer own it. This is how you do it: http://www.girlsaskguys.com/faq/features#157
You can disavow it, meaning the question will remain anonymous and you won't receive notifications from that question. To disavow a question, you should wait at least 24 hours, and click on the disavow icon that's found on the bottom right corner of every question on your list of questions.