When you get your grades they will be crap like you have suggested, compare your crap grades to your smart ass friends who get good grades. Jealousy should motivate.
Knowing that your grades are going to be pretty average/****(depending on how u see it) should be enough to motivate in itself. One of the best ways to motivate yourself is too look at some of the University requirements for your subject of choice.
Just become friends with a smart ass arrogant person, he will annoy you so much and make you so jealous that you will just have to sit down and revise.
Btw: When it comes to revision, do it atleast 3 days in a row, once your in the routine it will become second nature to you.