I'm was a massive fan of the plasma pistol on the first Halo. Strangely, I was also extremely good with it, if I do say so myself. I nicknamed it the "roomclearer" as it allowed me to unleash some berserker like attacks on entire rooms of legendary level elites and come out on top, simply by utilising the high fire rate if you can fire it fast enough. Its not the first time I've taken upwards of two legendary elites on with enemies supporting them and come out on top.
That was a "lethal joke weapon" in Halo 1. My favourite weak weapon was the omniwrench in Ratchet and Clank, and I often insisted on using it when I should probably have been resorting to heavier weapons. Needless to say I died a lot, but I just liked using it so much. I also often find myself using weak weapons, in games like Mass Effect and Saints Row 2 I use the pistol instead of the rifles due to familiarity with pistol weapons and a fondness for pistols going back to my Halo 1 days. I guess I just have a fondness for weak but early weapons I can get an insane amount of practice with.