A 79-year-old man was slightly injured on Saturday while waiting in his brand new convertible in a drive-through lane at Burger Prince restaurant. Herman Sherman of Northville suffered a mild burn about 9:00 p.m. when a young female employee accidentally spilled a cup of coffee into his lap. Sherman said the coffee was hot but not scalding. He refused medical aid, saying the only problem was the stain on his slacks, but it would wash out. He was given a fresh refill. Before Sherman drove off, the restaurant manager, John Johnson, gave him two free gift certificates--one for an extra-large coffee and one for the restaurant's newest sandwich, the McRap. The employee, who was a new hire, was let go later that evening. She was quite upset. She said she would probably sue Burger Prince for letting her go. She said it was the man's fault for ordering something that she might be able to spill.