"Hey, I have some cool picture to show you, but it´s on *insert random name of website*. Can I have your wifi password please to show you?" (or stg like that, it work everytime, but remember - when you´re at someone´s place, you´re usually there to share time with them, not with your on-line friends. Unless it´s a terrible family meeting then go ahead.)
-oh hey xxxx, can I have the wifi password to email/work/lolligag/do homework on?