Q: What can an actor do to help a comedy script/scene/moment that is just badly written or structured? What do you do when the writing is bad, but the director wants a laugh?
A: One approach is not to worry about what you say; focus on who you are. Always play the character. Think of your Mom, or your brother-in-law, or your dotty Aunt Ida. When they walk through the door, it doesn’t matter exactly what they say, or how they say hello. What makes them funny (in retrospect, at least) is who they are and the way they say things. As an actor, your job isn’t to write the script. Someone else is taking some heat for that. You’re job is to bring the truth and your perceptions of your character into any situation, and that includes what they’re saying and how they’re saying it. Another way of saying it is: find a way to be human, which means all that that entails: flawed, sometimes stupid, confused, exhibiting human behaviors.
There is one caveat: a script that’s overladen with bad jokes. The approach here should be that if you can’t pitch a better line to the director, then ask that jokes be removed, or better yet, get someone else to say them. De Niro and Eastwood regularly go through their scripts removing their own character’s dialogue so they can spend more time listening and reacting.