Backpack & frontpack & packs in pairs

“Have you seen that guy he had a backpack in front. Only that he couldn’t put anything in there.”
“A strange tourist thing. I wonder why they use backpacks, when they carry them in front. It’s not comfy.”
“Oh you haven’t seen him? I meant his belly.”
“Ha, this kind of backpack. I get it.”
“Yes. It looked especially funny because of the symmetry. A backpack and a frontpack.”
“The opposite of a sixpack.”