I have had a few moments like that in UT2004, back when my gaming community was still active. I had a trick that most people would usually fall for, even though I did it very often. The trick is to run away from your opponent as if you had very little health left. You then run around a corner, and as soon as you're out of sight, stop, turn around and wait. They, sensing weakness, will usually charge right after you, expecting you to be a lot farther away than you actually are, and expecting you to be facing away from them. The result is that they get a face full of flak cannon (for example) and usually don't have time to loosen a single shot.