Bobby had a terrible temper and used to routinely punch people out whenever he felt like it. Why is it then, that aside from one relatively early episode, he never hit Cliff? After all, Cliff did so many things to take advantage of Pam, he lied to her constantly, and most importantly to Bobby, Cliff actively tried to ruin their marriage so she would divorce Bobby. It would have been very satisfying to see Bobby treat Cliff the way he treated everyone else who did things to hurt Pam, his marriage to Pam, or even much lesser things. I found it out of character that Bobby let Cliff get away with so much regarding his interference in their marriage or even the many times Cliff mistreated Pam. Bobby made a lot of threats to Cliff such as how he would beat him up badly if he ever saw another tear in Pam's eye because of Cliff, but Bobby never followed through!