When you are looking for a synonym for "poor excuse," there are several options that you can choose from. One of the most common options is "lame excuse," which is often used in casual settings to describe an excuse that is weak or unconvincing. Another option is "flimsy excuse," which implies that the excuse is fragile and can easily be torn apart by logical arguments. "Inadequate excuse" is another possible synonym, which suggests that the excuse is not sufficient to justify the behavior or action. Finally, "pathetic excuse" is a harsher synonym, which implies that the excuse is so weak that it is not even worth considering.