If you want to Buy Things, but don't have enough Income, you may attempt to borrow from a roommate. You must make your request during your Action phase, but may choose to do an Activity instead of Shopping if no one agrees to lend the necessary Income. You may not borrow more than your total Income (since you have to pay it back the next turn), nor can a roommate lend more than his total Income. Lenders with variable Income must roll the Income for their next turn so they know how much they can offer. Once a player agrees to lend Income, you have the use of this extra Income for the duration of your Action phase.
During the Lender's next turn, his Income is reduced by the amount he lent. During your next turn, your Income is reduced by the same amount. If that leaves you with 0 Income, you cannot go Shopping or do Activities that cost money, unless you have a card that gives you a bonus to your Income such as Change in Couch. The lender, conversely, is richer, by the amount he lent, on the turn after his Income was reduced.
Example: Jon has a Campus Job, with an Income of 3. He wants to buy a GameStation, which has a cost of 5. He needs 2 points of Income, so Megan can't lend him what he needs (she has an Income of 1). Dan, the Web Designer, offers to lend Jon 2 Income. Jon has 5 Income this turn, and buys the GameStation. On Dan's next turn, he draws Shrooms, but can't afford them, because he loaned Jon part of his Income.
On Jon's next turn, his Income is reduced to 1 to pay back his loan. When it is Dan's turn, he now has an Income of 6 (his normal Income of 4, plus the 2 Income points Jon gave back), so he can buy Shrooms and also Cloves.
Players may decide to go out with one of their own roommates (i.e., another player). Both players must agree that they are going out, and then they become each other's Live-in S.O., following the same rules for Nookie as the Live-In S.O. card, except that both players receive Slack when either one plays a Nookie card. Each one decides separately whether to take the automatic 3 Slack for S.O. Nookie, or whether to roll. They don't break up unless they agree to, or if someone plays the Break Up card on them. If they do break up, each must discard their single highest-Slack Thing, because of the painful memories it brings back . . .