Superman was around and he heated the iced coffee with his heat-vision just for fun so that we could see what you were going to do next
So what you're saying, Clark, is that Superman was in on the joke and decided to hang around the Daily Planet all day helping screw with Jimmy (and making innocuous thought-bubbles in case Jimmy had become telepathic?), and you were the only one who noticed him using his heat-vision on that coffee? You who happened to be nowhere in sight at the time? You who have just the right hair and build for Superman and would in fact be a dead ringer for Superman without your glasses?
What a funny coincidence! Let's all laugh and go get cake!