Don't sit on the toilet and practice...
For me it's drinking. I can smoke up some doobers and then lay out righteous riffage all day and night but as soon as I drink alcohol I just don't feel like playing. It doesn't make sense to me why, especially because I love playing when on other varieties of intoxicants, and I know loads of people like to drink (in moderation) when jamming, but if I have even a couple beers I just put down my guitar.
Gotta love that headspace bud puts you into when you're riffin'
It's pretty fun to play when you're buzzed and you're jamming with your friends with the exception of screwing up a couple times but not noticing