There is the obvious issue of plugging the mains connector into a speaker socket and toasting your drivers with an entertaining (for others) bang and a flash, but then there is the far more dangerous scenario where one box is linked to another box with something like a Speakon to TRS cable (we've all done it
). Now plug the power into the speaker by mistake and you have a TRS 240V death wand 
. If you think this is unlikely let me regale you with a little tail! This happened on a gold mine I was working on. An operator noticed that the cyanide was not flowing into a tank at the correct rate. After checking the pumps and valves he decided to try and blow the cyanide pipe clear with compressed air, He removed the standard pneumatic fitting from the air line, fitted a new fitting to suit the cyanide pipe, turned on the air, and went to investigate the situation. Now as you all know, air can be compressed, cyanide cannot, especially with a positive displacement pump (look it up), so all that happened was the cyanide decided to go and have a little look at the pneumatic air network and got pumped everywhere including into pneumatically operated valves and into air supplies in the laboratory and workshops! Cyanide, my friends, is VERY nasty stuff and gives off a lovely sleeping gas when exposed to air, unfortunately there is no wakey-up antidote for this kind of sleeping. All this because someone used the wrong connector! 
