I use the word shanagains all the time. Seriously. I say it at least twelve times a day. To everyone.
I've even got co workers to start using it.
Also, I use SUPRISE BUTTSEX all the freaking time too. It's actually terrifing. (Mostly because my co-workers have started to pick it up and then one or two, who I am really great friends with, smake my ass and yell, SUPRISE BUTTSEX. Tis, sad. Really!)
As to where the this to silly saying orginated from, well, Shanagains is from an ex, he use to say it all the freaking time, but when I moved away from home and got resettled I promptly forgot, till one day someone said to me, what are you up to? And I responded Shanagains! Thus I have used it for nearly a year, almost everyday. To the point where when people hear it? They think of me. Heh.
And Suprise Butt Sex, comes from the sweet internets, I saw it and used it. And loved it.