Gee, What does "Johnny on the Spot" mean?

LMAO.
We host an annual Christmas dinner for the family across the street. They have three kids we have watched grow up, and they are all so nice. Anyway, this year we went to On the Border. I whispered to the young waitress that it was a special occasion, and I would really appreciate it if she was Johnny on the Spot for us. She said "What does that mean?" I explained and after laughing, she did an amazing job for us. Our friends wondered what I had said to her, so I told them. Both parents (around 40) and all three kids (13, 16 and 17) had no idea what Johnny on the Spot meant. The kids thought it was like a portable john. We all had a good laugh over that..