Went for a meal last night with a few ILs and another family (the parents and aunties/uncles of the partner of an IL) - about 20 of us in total.
We went to an Italian chain restaurant. I am pregnant so not drinking and DH in his support is abstaining from drinking too (his choice before I get flamed!). We had 3yo DD with us.
We had a pizza each (£9 each) and DD shared mine as we both have quite small appetite, and all 3 of us shared a bottle of large mineral water which was £3. DH and I shared a dessert which was a fiver.
The rest of the table all had a 2-3 courses each and every single person had lots of wine, ordered in bottles
Now I am usually happy to split the bill and think nothing of it, when people have similar food and drink. If I had to pay £5 more than I would individually it doesn't bother me at all, I don't like to make a fuss.
However when the bill came someone in the 'other' family took it and got his calculator out....£33 each! "Oh actually it's probably not fair that Pinky and PinkyHusband pays that for MiniPinky. Just pop a tenner in for her or something and I'll recalculate" 
I would rarely spend that much on a meal out. We are saving for the baby and also have had lots of unexpected bills lately - car repairs, things going wrong in the house, broken washing machine etc. We budgeted for the meal but thought more around £35-£40 for the 3 of us.
Anyway, as DH went to put £76 on his card as we didn't have enough in cash, I said "sorry it's just that we didn't have alcohol and shared most of our food, is everyone happy I we just stick £40 in?". Which was £14 more than what we actually ate and drank.
There were some pissed off faces but they said "oh I suppose so". Everyone else had to pay £3 more each
DH thinks for the sake of an extra "few quid" we should have just maybe left it, but I think I was in the right and they were being cheeky fuckers.
WIBU and tight or would you have done the same?