make a joke of (something)
To mock something or make something a subject of humor, especially something that should be treated seriously. You shouldn't make a joke of suicide—Tom's mother took her own life when he was still in high school. It's great that they can make a joke of this, but we could all be fired if something doesn't change!
make a ˈjoke of something
laugh about something that is serious or should be taken seriously: Don’t make a joke of it! I could lose my job because of this!