"rocket lawnchair" is basically another way of naming the n00b wep0n of choice in fps games like halo 3,cod4, and shadowrun. actually saying the word instead of saying rocket launched acxtually results in more lulz..
The act of sitting on a lawn chair or similar in the bed of a pickup truck or flatbed while being driven through a tourist trap, park, or other sight-seeing location. This experience is enhanced by drinking beer and/or smoking cigarettes as one is driven around.