Caffeine has practically no effect on me whatsoever.
I have a slightly high tolerance to alcohol, and I haven't really noticed any fundamental "personality changes" while drunk. Lowered inhibitions, but that's part of the effect and should go without saying.
I don't feel the hyper or being awake late thing from caffeine, but when I was in college 3-4 mt dews a day was enough to send me to the doctor because my heart was skipping beats. At the peak I was missing a beat every few minutes. Scared the hell out of me.
I had to go cold turkey and after like 2 weeks the heartbeat skipping had gradually gone away just as it had built up before.
I am not sure what type I am, but yes I am sensitive to both caffeine and alcohol. When I drink a lot of alcohol, I usually wake up the next day with awful anxiety. Also, when I drink a lot of caffeine, I usually get very anxious as well.
I don't drink coffee or alcohol any more because they have such a strong affect on me - I can get drunk after only a few sips of an very weak alcoholic drink and strong caffeine makes my heart beat really fast and makes me feel dizzy. I find that even chocolate has a strong affect on me and all sugars, so I eat them in moderation.
I also got really bad hangovers from alcohol, even if I drank lots of water. Once I got a hangover that felt like serious flu after an hour...
If I consume too much coffee, forget about it folks! I am totally wired and I end up feeling achy and fatigued not to mention my heart-racing. I end up shaking a lot, and conversely I end up having my mind running a lot more into even more baseless thoughts based on nothing more than fear and anxiety.
If I have too much alcohol, well then I am miserable as piss. I end up becoming really grouchy and testy towards people. So my limit, rather threshold for alcohol is very very low. I also end up with a headache, which only makes my bad mood worse.