Bloodex said:
I'd say you need to reach a fair level of drunkenness (as in, actually drunk; with most people, tipsy won't do it) to experience a noticeable hangover. Bear in mind, though, that this is coming from someone with a good amount of alcohol experience. Adding onto what Jake said, one of the huge tips I'd use is to not mix your types of alcohol (don't confuse this with mixed drinks - those are fine!). This is mostly from personal experience and the experience of some others, but I find that if I stick to just one type of drink, I rarely get hungover while if I have several different types, I'm a huge mess in the morning. Really, though, the key to avoiding hangovers is careful moderation while drinking.
As for your other question about how obvious it is - it's obvious if someone knows you well and knows what you're like under the influence of alcohol. Given what you've said already, people don't know the second part of this so they might be able to guess. Or, they might just think you're in a really good mood! In any case, if you only drink enough to be on the edge of tipsy, the feeling won't last long and you'll soon be back to your normal self and you may not even end up drinking that much. Alcohol doesn't have an instant effect and small quantities of it may have no effect at all! Honestly, I'd recommend you don't aim to get tipsy at all, were you to drink at this party.
What Jake said applies again if you want to drink alcohol and avoid changes to your behaviour; eating before drinking provides something to 'soak up' the alcohol and staggering your drinking with water will dilute the alcohol and make it have a lesser impact on you. One thing to note, though, is that alcohol is a fairly powerful diuretic - constant toilet breaks is a fair sign that someone could have been drinking, and a lot of water won't help you hide this very well. Once again, though, drinking carefully is the best way forward here!
