Soft Drink Tilt Level Indicator

I like fizzy pops. When I've drunk about a two thirds of my soft-drink, I like to tilt the can on to its corner and impress the ladies with the magical tilting can party trick. (It's even more impressive to hold an imaginary thread above the topmost part of the can and pretend you're supporting it that way -- I've had one or two fans pass out at the shear brilliance.)

The problem with my trickery is sometimes I judge the level wrong and leave a nasty wet patch on the front of my trousers. This, I've learnt, doesn't impress the ladies.

So, what I'm proposing is a very small plastic window in the side of a regular 330ml can, about a third of the way up, marked with a simple line passing horizontally across it so that one can see the optimum level for the noble sport of can tilting.