Superman being made into a vegetarian in Birthright is hilarious, considering that Beef Bourguignon (or whatever that dish is called) has actually been called out on many occasions over the years as being Clark's favorite food, as well as being a relatively big plotpoint (considering it's a food) in the "'Til Death Do Us Part" story, as it was the password between Lois and Clark to let each other know if one of them was ever being impersonated.