I do have experiences like that, someone owes me money, a member here in the forum who I got friends with owes me a total of 0.3 BTC, an RL friend owes me around $10k and both did not pay. It was also part of my collective winnings in gambling years ago. Despite that, I am still convinced that people are generous and at the same time selfish.
You were kind to have given a helping hand to friends at the time of need when you had it. They say what are friends for but unfortunately the friends have decided to take your winning that you are suppose to use in buying something tangible to remember your winning. Next time you don't have to give people that won't return your money if you want to collect it back. Or you use escrow for such loan.
Yes, that's right! Although we are not obligated to help people in need or friends, there is some voice deep inside us that wanted to help even though there's no assurance that we could get back our money at any given time and that is fine because we are human beings who want to be kind and hospitable at the same time but some times people or even friends take advantage of that and just using the term friends or just like the saying you said above.
Its understandable that there are things which would really be pushing us to help despite of those probabilities or chances on getting abused thats why you should watch out for that.
Going back into the topic about most expensive thing been bought then there's nothing on that because whenever i do make huge wins then i do just simply hold it out and
later on i might consider on buying something but after all the things been purchased i had forgotten on what are those.
That is natural these days, there will be always some kind of people who will take advantage of you and of course you won't know that as you will only know their true motive after the fact but anyways, that's fine as long as your heart is open to help but you still really need to be careful for these types of people because they are literally everywhere.
As for me, haven't bought anything expensive really and sometimes if I win, I'd use it to pay some bills and take my family to some random restaurants if there's some spare left.
. After borrowing money and the due date came, none of these two ever message me or voluntarily talk to me and say that they can't pay their debt. The worst is my RL friend even put me on ignore in messenger when I asked for his payment while the one I met here admitted that he just can't pay the 0.3 BTC due to his current situation. 
