How do you guys usually do this?

When I am flying with just one passenger, and it's a smaller plane like a C152, I usually determine how much is too much and say that as long as you are under 250 lbs, we are good to go. But I am planning a flight with 3 of my friends in a 4 seater plane and I can't do the same strategy since each person changes the weight and balance (you can only guess for one variable... not three).

So, I committed a cardinal sin and guessed their weights (above what I expected them to weigh to err on the side of safety). Then they saw my paper and asked me about the weight and balance and how much I thought each of them weighed for the flight. I showed them my sheet, and they got offended. I don't think they were offended at how much I guessed, but just that I guessed in the first place.

What's a seasoned pilot's advice on this issue? How can I make it less awkward but still obtain the necessary information?