I choose GMT/UTC for things such as my digital camera clock and IRC timestamp. I screw up the order of words when I last started irssi from the Terminal of my iPhone, because it’s something I do once a year on average (it was already something to remember the timezone command, it would have been a prowess to type the whole command in the right order ;)).
Here’s how to set the irssi clock without having to quit:
/script exec $ENV{'TZ'}='UTC';