I can't imagine that being the result of two random comets colliding: they'd blast each other to bits unless their relative motion was very small. Some suggest it used to be much bigger and blew out stuff on an earlier pass by the Sun, excavating odd shapes (and a waistline) in the process. Could be. The thing shows divots that might be the effects of an earlier fly-by.
I wonder how much bigger it used to be. Suppose a big soft blobby pre-comet swung by something heavy fast enough for tidal effects to break it up. Quite a bit would be lost, but some of the residue might coalesce again, maybe into a couple/three clumps. Say 3. They orbit each other, and the "chaotic" motions of the 3 bodies bring two close enough to impact. I'd naively think it wouldn't be a harsh impact--the bits might stick together. Then swing it by the Sun a time or ten and it might look a lot like the duck.