Back to the Future (1985)
Although this was unexpected, George is trying his best to be bold and messing up in the process could conceivably be in character. The error is in Lou's reaction. We've already seen that he has no problem speaking his mind and gets aggressive over very small things. He would not have just calmly and quickly looked at the mess and started talking to a customer. At minimum he would have got a rag to start cleaning but most likely would have yelled at George. Obviously the actor playing Lou, Norman Alden, didn't want to ruin the take and just ignored it as best he could.