You can always do this...
Roomie, "check out my holiday soda! Want one?"
Pour yourself a full glass/open a can
Take a sip
Quickly dump soda out. Upend the can over a plant, dump the whole glass into a sink, the intent is to give the impression you can't get it away from you fast enough. Spitting out the sip you took is optional.
Exclaim, "yuck! That is absolutely awful! Who would make that? How can they sell it? No wonder you sere pushing me to take one, you're trying to get rid of it!"
That's actually fairly close to how I responded to one of those holiday sodas and I was being totally honest (and I like good soda).
For bonus points you can spend the next few weeks laughing about "Now with extra Holiday Chemicals! " in a faux tv ad voice and the like. If you dumped the soda over a plant, make a show of periodically checking to see if it has died.
A variation of that works on mac n cheeze too, but to do it right you must regurgitate the food back onto your plate. Tricky but it can be done.
Yeah I'm an awful person.