Your tolerance changes from day to day, depends on all kinds of things... mainly what you have eaten and how your adrenal glands are doing that day.
I have had days where I could drink a water tower full of moonshine and be fine and then had days where I had a single IPA and I'm slurring my speech...
I don't think you should gauge how somebody is acting under the weather as their personality, as it is more like a mood in that it's a temporary state of mind, really just like how hormones influence moods... well it's the same thing as alcohol influences your glands which influence mood. Now if they always act like a d-bag that's another thing!