Friendship Reciprocity Ratio

The friendship reciprocity ratio, or F.R. Ratio, is the ratio representing the unwritten friendship law that the sum of x-friend's purchases for y-friend should be equal to, or as close to equal to, y-friend's purchases for x-friend. The closer to "0" this ratio is, the more substantial the friendship. Any friend who is significantly negative in this ratio is a shitty friend.

Dave- Dude, Greg "forgot" his wallet again. Had to pay for his lunch again. Not to mention I bought him an Audi for his birthday last month and all I got was a misspelled "Hapie Berthday" on Facebook today.

Nate- Greg is a shitty friend. What's your guys' friendship reciprocity ratio at now?

Dave- I think he's got our F.R. Ratio down to -$3,000,000 now.

Nate- Wow dude, what a piece of shit.