The first time I had my shot, with a nurse in the room, I literally geysed blood. Like it was a spurt out like in a cartoon.
The nurse rolled her eyes and said, "Typical. I don't put gloves on because you're injecting yourself, and of course this happens." There was a biiit more than a dime sized amount of blood, and she was laughing about it with me, so I really wouldn't be concerned.