I know the game is called 5-lies but is it strictly necessary to disclose how many questions were going to ask her or could I simply word this by saying I'm going to ask a 'few' questions?
If she happens to be successful with all 5 questions (if she may have genuinely played this before) and let her feel like she's won, commend her, saying:
Me: "WOW I've never been beaten at this before... ok... *look of graceful defeat* what's that you're drinking?" *discretely pointing at her glass/bottle then proceed to grab my wallet*
(I'd only ever plan on using this variable if she already has an easily recognisable drink)
HB: 'it's a...'
Me: You know what? *puts wallet back in pocket* that sounds wonderful - Thanks very much
BAM! (Game over)
I really like the structure of this routine, but even I've heard this one before so to me it seems a little 'canned', so I'm aiming to put my own unique twist on this one.
I know this isn't 100% fail proof either as she may want something different and say "actually I'll have a ... instead" but if this was the case, I see this as an opportunity to 'lead' her to the bar, away from her friends and make her further qualify herself before I actually buy her that drink.
What do you guys think?
I think the specificity is important to get her to take the bet in the first place, and I highly doubt that she will want to play it if she already knows it. Anyway, would you take a bet that involved asking you a 'few questions'? 'A few questions' is a phrase that signifies something long. It's what an experimenter says when he wants you to take a lengthy questionnaire, what a salesman says if he wants to sell you something over the phone, what a police officer says if he wants to interrogate you down at the station.*
Also, I think the number of questions is very purposefully chosen, because it is actually not five questions that you are asking. Only the first three questions are serious, the fourth question is where the game ends (unless she's smart, then you'll have the fifth as backup). So you're not asking five questions, you're asking three plus one questions, if you catch my drift. And why is three a good number? Honestly, I don't know, I suppose all good things come in threes.
*Note that this is usually also true of examples.
EDIT: And if you lose, you owe her a drink. The purpose is to talk to her, not to get a free drink, so I would still consider losing this game a success. (Also, I would pretty ruffled if she lost and refused to pay my drink.) For full disclosure, I have never used this particular party trick, these are just my thoughts.