Well, it is annoying as all getout so many will be tempted to destroy your motor lol
If yer gonna do that, I would mention drilling a hole(s) in the end cap and putting it back on and/or removing some of the baffles. This will provide some backpressure and tone down the noise a bit.
But really the best/only way to go is to get a tuned pipe, Sick Bike Parts has one that works really well with a pronounced power gain - many have adapted the cheaper pocket bike pipes to fit.
It may not be illegal to run w/o the endcap - but man, people will hate you o.o