The condition in which a man has three testicles. One could be considered tri-packing if he has two and a half testicles, as well. The half testicle is usually about half the size of a normal testicle, but still a third testicle. It's often connected to the normal testicle and looks like a multiplying cell just before it divides.
Sometimes this is known as a tri-blossom.
She assumed he had a huge package, but then his girlfriend revealed that it just appeared that way because he was tri-packing.