Is marijuana bad to smoke every once in a while?

A little. There is no safe level of exposure to smoke. Otherwise, occasional use will result in cognitive impairment (being stupid) for at least 24 hrs after each use. Each person has to decide how good or bad that might be.
Joint. Short-term effects are noticeable, but in the long run & with continued use, it will start to become a habit & affects u physically as well as emotionally/intellectually. Refer to my answers on Marijuana effects.
Marijuana effects. "smoked marijuana damages the brain, heart, lungs, and immune system. It impairs learning and interferes with memory, perception, and judgment. Smoked marijuana contains cancer-causing compounds and has been implicated in a high percentage of automobile crashes and workplace accidents.".