DIDN'T:
Lucifer gives an excellent answer to the question (E. Carefully think out your policy to make sure that what action you take against those accused of such crimes has the backing of solid evidence, is a precise military target and not increasing suffering, and will not pull apart the world order, thus carrying out positive action which achieves long-term results and achieves more than short-term revenge.), but if he was too articulate for you then the answer is G:
Find the right people and punish them hard, while maintaining your morally unassailable position by seeking to minimise innocent casualties and by putting right some of the underlying causes.
If we are going to set ourselves up as judge, jury and executioner then we must at least follow due process. Regardless of the awful scale of this horrifying and tragic outrage, we must not be blinded to what is right. (You asked BTW for a definition of cowardly - anything which is not morally courageous. Thus the terrorists on 11 September were the worst kind of cowards, while any politician who follows the line of least resistance and maximum popularity, and shies away from what may be right but unpopular, is also displaying a lesser form of cowardice.)
Some of you may have been happy to murder whoever you thought were the guilty men of Omagh, and some of you may be happy with the thought of slaughtering any of those who don't agree with you 100% and who perhaps even supported the aims (but not the methods) of those responsible for 11 September. I can understand anyone being angry at the sight of Pakistanis buring Bush in effigy, or Palestinians holding up V signs. But that doesn't make them legitimate targets. Fortunately we live in a civilised society where justice must be seen to be done, not merely revenge.
There are some fairly far-fetched and facile comparisons and illustrations being used, and some fairly offensive assumptions about what kind of people those of us are who feel uncomfortable about the no-brain gung-ho "let's bomb Afghanistan into the Stone Age" cliches and neanderthal rhetoric being used here, too. But if it'll please the simple minded, if I was burgled, and my wife and family brutalised, then I hope I'd wait for the law to take its course - or at the very least, I'd make sure I beat the crap out of the right person, and not just pick on someone against whom I had a long-standing dislike. That would just make me a thug, a vigilante and a criminal.
This isn't some half-baked Hollywood movie, and making light of the situation (as the title of this thread does) is unhelpful. Calling these people perps is another indication that immature and inappropriate TV-show metaphors may be being applied. Innocent lives must not be shed in the search to achieve justice for the innocent lives already lost. America sets itself up as the leader of the free world and the shining example of enlightened democracy. Kneejerk revenge is not appropriate from such a great nation, whereas legal retaliation may be. Without following due process, we diminish ourselves and play into the hands of those who seek to destroy what we stand for.
I fully support effective action against the guilty, but like many Brits, I feel uneasy when our PM writes a blank cheque of support to the USA when that nation's language is so (understandably) intemperate, and when justice and retaliation appear to have been put behind the desire for pure unadulterated revenge. This is not Kuwait in 1990, where there was a 'smoking gun', and when I fully supported all actions that were taken (and indeed condemned them for perhaps not going far enough). I am not some bleeding heart liberal who thinks that military action is always wrong (or even regrettable), I just believe in international law.
PS: Desperado. I'll argue with you when your geopolitical outlook progresses beyond about 1975, OK? This isn't 1967, and Israel's neighbours aren't bent on its destruction, 'kay???