This happens to me all the time, I figure the camera's round hole is the problem. The lens is round, the hole is round, hence there is no grip.
Here is what I do, I park my pick-up on hill and set my new lens behind the tire, take off the brake, and by doing that, it bends the lens a tad. Now when I put in on the camera, it takes a lot of effort, I even have to use a crow bar sometimes. Once it's on though, it never comes off.
EDIT: Steve makes a good point, the key word is black duct tape, as the silver stuff comes from south Artica and is known to carry disease. Would you eat a raw chicken, NO. Same thing. I guess you could hold the camera away from your face and about two or so feet away, but that is more of a preffisinal thing.