The thing is, people who steal food from communal fridges are the same people who can't be arsed to do the household accounts when it comes to splitting up the utility bills...
I'll bet your son ends up being the sensible one who does all that.
Oh god. Flashbacks.
My final year at university was notable for, amongst other things, developing altogether too much familiarity with Microsoft Excel than is optimal for one's mental health. The products of this were twofold:
a) A time-domain modelling of a cognitive neural network
[1] on a scale that struck fear into the heart of Clippy and excessive heat into the woefully inadequate cooling system of my AMD Thunderbird.
b) The Grand Unified Spreadsheet of Doom. In which I decided that while all housemates had contributed by paying some utility bill or other, they weren't going to cancel out, and the only way to work out who owed what was to go through the entire archive for the house mailing list (we were geeky like that) for the last three years and spreadsheetify all bill payments. This worked surprisingly well once we persuaded the resident hobbit to tell us how much he'd secretly spent on water bills and council tax.
Needless to say, b) was much trickier, but sadly didn't earn any credits towards my dissertation. A discrepancy of several thousand of your earth pounds eventually changed hands, and while I was tempted to levy a hobbit tax
[2] in the murky depths of some calculation that nobody would ever be arsed to check, I decided to take the moral high ground and be glad that I'd had the foresight to pay the ludicrously expensive ADSL bill, and was therefore on the receiving end of some of the payments.
Which, with hindsight, was bloody stupid. Especially as I did most of the cleaning, to the point of ending up on steroids. I'm sick of being the sensible one.
[1] My advice to anyone ever contemplating modelling neural networks in Excel: Don't.
[2] I figured I was probably entitled to compensation for having to deal with the effect on the drains of the insoluble residue formed when the hobbit's vegan soap mixed with the Canterbury carbonate in the water.