Jager tastes like crap. Redbull tastes like crap from crap.
Sour drinks work.. but you could go with something like a smirnoff ice or hell a wine cooler. If you are into making stuff there are a ton of drinks you can make that are fu-fu. Mudslide, Irish Coffee, etc.
However, ask if he's a real man and try to push something on him with some kick if he's going to be drinking. Straight up vodka, tequila, rum, or whiskey. Hey mix all four of those and you get 3 white men and a beloved patriot!!! throw in on gin and you get the four horsemen... muahah. Or ask if he wants a Bartenders Towel.... Rookies need to be initiated haze style.
Then after he gets hammered... make him take a Muff Dive. Incase you wondering what that is... it's a big bowl you put some brandy at the bottom. Then you use whip cream on top and put a cherry in the center. The purpose of the drink is to get the cherry out without picking up the bowl or using hands. It's frikking hillarious watching a drunk do this.
Follow that up with a Cement Mixer... umm umm good!