I was introduced to the following technique by the archcricket of Wales at a charity luncheon several years back – it can cause terrible internal consternation in the mind of the poor victim and will surely leave them on edge for the entire evening. It is primarily intended for the restaurant lunch-for-2, with a target who is sensitive to matters etiquettical, otherwise they might miss it entirely, and then where would you be?!
When you sit down with your partner at the table and are ordering, be sure to ask for a jug of water; (Oh! the other person must also be wiling to drink it elseways this will not work at all). So yes, anyway. You are to keep track of the levels of both his and your glasses of water during the meal; what you are waiting for is a time when you are just finished yours, and he is somewhere between half and two-thirds finished his.
Now, when you reach this point, you reach for the glass and fill yours to a level just slightly below the level his is at, and then you put the jug back down (Do try to make sure they notice this; but don’t point it out in some vulgar way). Then you carry on. Such an action will cause immense conflict in their refined minds as, on the one hand, you aught have topped them up, but on the other hand you seem to think such a quantity as you have poured to be sufficient for your own purposes. I am not, maybe, best able to explain the psychology of it in words directly, but I will vouch for its fantastic effectiveness.