|Images copyright Alexandros Grigoropoulos|
If riots are made-for-TV spectacles, then one would expect the biggest ones to occur on Saturday nights since Sunday is still the biggest day for TV viewing.
Friday is called "Where news goes to die". If you want to announce something that you hope is soon forgotten you announce it on Friday at 3:00 in the afternoon.
Useful information? Marginally. If you MUST go to town then Thursday is your best bet and Saturday evening is your worst if you want to avoid spicy-times.