I think everyone has bought juice like that.
The term you'll hear a lot is "steeping". It's misused, but what they mean is that you need to let the juice air out and age a little. Either remove the cap and let it sit overnight, or remove the cap and squeeze out the air and let fresh air in once a day for a few days will fix the issue. Letting the juice sit longer and shake the bottle once or twice a day will usually help enhance or improve the flavors as well. In some cases letting the juice age a month or more can really improve the flavors, especially in juices that use vanillas and custards.
And always remember to give the bottle a good shake before using it. Both flavorings and nicotine settle in time so the juice at the top of the bottle will be weaker than the juice at the bottom if you don't shake it up.