Richards, to his credit, was the best of the four by far of not breaking character. I have watched the outtakes and bloopers more times than I can count, and he would get frustrated at times when someone would break, but hey, JLD once said that no one was a bigger fan of the show than they were, so the cast knew that what they were doing was hysterical, and they knew it in real time. And it is human nature. When something is funny to you, you laugh. I always find if fun to re-watch episodes and try to find moments where someone is close to breaking character, or even doing it a little, like when Jerry is trying not laugh at being read the riot act by the library cop, who ad libbed the line, Sure, go ahead and laugh if you want," because Jerry was legit trying not to laugh, or the scene where Jerry notices Kramer's teeth are discolored due to smoking ("Look away, I'm hideous!"). There are several sudden camera angle changes in that scene to where I always think they had to cobble what we saw in the episode from God only knows how many takes.