Here's the easiest way to figure out how rich or poor one of your friends is: write them a check for $300 and see how fast they cash it.
1 day: Broke as hell. You probably saved them from their 5th overdraft fee this month and paid for their meals for the next 4 months. Expect to see a LOT more of this person.
2 days: Fairly desperate for cash, but not enough to go straight to the bank and miss the one day of the week when they can really try to forget their life: 20 cent wings and dollar drafts at the local bar. It will be the first thing on their mind upon sobering up the morning after though. Wondering how the hell they got such a cool rich friend.
3-15 days: Not quite living life hand to mouth, but considers the check to be a significant chunk of the rent this month. Actual number of days depends on just how close to the day rent is due you gave them the check, or proximity to a holiday or significant other's birthday. May consider the check to be somewhat insulting, since they "can make it on their own."
16-45 days: Has already built up a decent emergency fund in case of a layoff. Will probably put this check to use on better than average dinners on the next vacation. Assumes that this is a guilt check from the time you slept with their significant other, but won't bring up the question.
46-90 days: Definitely not hurting for money. Probably bought some designer shit on a shopping spree in the last week, and might drop your check on a bottle in VIP if they get drunk enough. Might consider the money to be payment for some bet they won but forgot about.
91-180 days: Has access to a limited trust fund, is dealing drugs other than marijuana on a regular basis, or just loses shit constantly. In the case of the former two, will be totally confused why you'd think they need the money, but will probably get you into VIP at the next super exclusive club party or hook you up with a bag of coke. In the case of the latter, probably broke as hell for reasons exactly like this – will beg you to write him another check because he lost the first one, then cash them both a day later.
181+ days: Filthy rich, how do you know this person again? $300 to them from a friend is just a thank you note; they would never actually cash it. The check is already void anyway.
Of course, if you have $300 to blow on figuring out if somebody is rich or poor, I think that says more about YOUR wealth than anything.