I know the feeling! Ten years down the line since diagnosis, I've worked out a strategy. I try and eyeball what's on offer, decide what I'm going to have, help myself to one plateful (and stick to meat, salad, a bit of bread and butter because it's an easily guessable amount of carb) and inject for that plateful. The thing I have to avoid doing is picking at bits of pork pie, quiche, etc, when you've no idea how many carbs are in them, and no idea how much you're actually eating.
Actually, the worst thing I find, come to think of it, is being involved in the clearing up. It's so easy to pinch the last bit of pie, quiche, sausage roll etc from a plate as you're sorting stuff for putting away or chucking out.