I think at Ducks death was the most Pain-inducing thing so far just watching the life slowly drain out of a young kid who about 3 or so hours ago was playing Batman and Robin.
Also i let kenny shoot him because not too long before i had seen the film "Of Mice and Men" and it reminded me of a
scene where The old Farmhand Candy is being pressured into putting his dog down and instead lets someone else do it (Similar to Lee pressuring Kenny into dealing with duck and then Lee saying he will do the deed) but afterwards he regrets not being the one to do it.
I don't think TT did take inspiration from that movie but it was quite similar.