Almost all of the following reactions are very deadly
* The Production of nitroglycerine.
* The preparation of Milions reagent using mercury
* Reaction of Potassium Cyanide and with Nitric acid.
Just to mention but few but let me explain the first one.
The production of nitroglycerin; It is made by slowly adding glycerine to a mixture of about 50% nitric acid and 50% sulphuric acids.
The reaction extremely exothermic in nature and so the temperature and pressure in the reaction vessel has to be correctly controlled because if the temperature rises above about 22 degree celcius, you run the risk of explosion.