Fun example about lazy teaching: Our undergrad's HKN chapter kept a test bank of past exams in Physics, CS, etc. When I was studying for my Physics final I went back to past midterms and realized the professor recycled questions from previous years with some numbers changed up. I ended up filling my entire cheat sheet with the questions that weren't already on midterms but were in the test bank.
The result? The final contained a majority of questions from that cheat sheet. I still pose this scenario to a couple friends nowadays asking if this would be considered cheating, and the responses are actually a mix of "no, you're just taking what's publicly available" and "yes, you're manipulating the system to get where you are and taking spots from someone with academic integrity".