Lucky you were thinking about it and realised, that cup would have kicked hard in your hand haha.
When I first started playing around with resins I had a cup of regular laminating epoxy exotherm badly on me once. 40 degree day and I mixed up a litre of the stuff in a tall cup. Put it down on the table and went to grab a brush, came back to find the cup melted all over the table and smoking badly. Infra red thermometer told me it was 213 degrees. All happened in the space of 30 seconds too. Lesson learned.