if you're talking plastic, use a bandsaw. If you're talking glass, use a diamond table saw.
If you're talking about a glass bottle, I'd suggest trying to score it lenthwise, then use the technique of thermal shock to snap it in half. That is when you heat the line with a candle, then dunk it in cold water, it should snap down the score line.
Try filling it full of water and freezing it, then make a jig.
don't do this as water expands when it freezes.
and glass doesn't expand.
pypers solution looks good
if it fails though do this
cut a big hole in the side of the bottle (like canoe) but leave the bottom half (and more) intact
fill with water to the wanted height and wait for water to calm down
spray graffiti paint on the walls from inside so that it paints them above the water (a bit is enough and not too closely to not disturb the water)
wait for graffiti to dry
spill out water