Shorting batteries is also never a great idea, but supercaps are more dangerous because of their low internal resistance.

This video is a good demonstration: https://www.youtube.com/watch?v=EoWMF3VkI6U

I was working on a controls project where we had large banks of supercaps that would charge up to ~900v. Have to treat those with some respect. However as long as they are kept cool the caps had no trouble being charged and discharged with a couple minute cycle with each bank providing 2kWh of energy. In the particular application I was working on we actually had 17 2kWh banks providing ~34kWh of energy every couple minutes. Would not fit in a cellphone though :)