I bought a whole bunch of sugar free red bull last year or so but did not drink the rest of them. Now i want to and i see that it says its expired july 2013 which is about 4 months or so. Note i left the red bull just like that in those 24 packs where i have about 12 left. Is it safe to drink it? I read that it should not be a problem since the date it says is usually best before the date?
Yes its fine to drink.
The taste may be slightly reduced or altered.
But there will be no fermentation or other growth.
It would smell and taste very bad before any significant microbe growth.
Depending on how it was stored you may want to reconsider. Aspartame does break down at high temperatures, I don’t know how this would apply as I just considered it something not to cook with, but if stored in a place that gets lots of summer sun heat it may be good to do a bit more googling.
There’s a difference between Expired and Sell by dates.
Not sure what Red Bull uses but I suspect it’s fine to drink.
It will still give you wings, but they’ll be bat wings instead of bird wings.
How is that different than how it usually tastes? 
I used to work for a Red Bull distributor and I always thought it tasted worse than vile.
Gotta agree. That said my experience with expired aspartame ( sometimes even just close to expiration ) is that the sweetness turns to a flavor very much like dirt. I have no idea if that is an idiosyncratic reaction or what, but from long experience I have learned to always check diet drink expiration dates and never touch one that is very close to or past it.