1. While going to school using the post 9/11 GI Bill (tuition 100% paid for, plus $1500ish monthly living allowance), found out I could take out student loans and the school would cut me a check for all the money the GI bill paid them...did that, bought lots of high-end outdoorsy gear (used for the degree, but not necessary) still paying off the loans. That degree got me a job that will allow me to have the loans paid off 5 years after graduation, but I could've done it all on the cheap and graduated debt free.
2. In 2010 I took a 2004 Ford Escape Hybrid that I had bought with cash to the dealership and traded it in for a GMC Seirra Denali & a car loan. Originally an effort to live out of a vehicle, but such a dumbass move on my part. It was so shiny!
3. Bought another Escape Hybrid (loan), wife liked it so much she stole it from me, so I was driving her paid off 04 Suzuki Forenza (4 door manual, great gas mileage). Sold that for cash and bought a pickup truck + loan. wtf?! I never learn. Used the truck a lot, both to move and for helping friends out, but still not necessary. Started cleaning up my act, found this site, and started telling my wife I'm going to sell the truck after it's paid off, and bike. Oh yeah, if I need to drive someday, we'll get a small, manual car (she said: "Like my Forenza?" hahahaha).
I wish the lessons I've had to learn hadn't been so expensive.