Sorry to hear that. If he poured straight vegetable oil into his tank with no filtering and heating modifications it would not take long for any oil to destroy a diesel.
Where you get your used oil is crucial. I have not heard about acidity as a widespread problem with waste v.o. - since every batch will be different depending on what was cooked in it. American food reuses oil too many times and has too much salt in it, and is frequently hydrogenated. All bad for engines.
My collection preference was Thai restaurants. The oil was used only once, very clean, and was a pale yellow color.
While it's true that once you get a spot of oil on your clothes it (and the smell) will never come out, vegoil fueling can be as quick and tidy as petroleum fueling. The learning curve is straight up to figure out a good system and many people give up before they get there.
VegOil is a fringe alternative fuel that has yet to reach parity with Biodiesel in public understanding and acceptance. The onus is on the individual to develop workable solutions for collection, filtering, fueling, and paying road tax. Until SVO is officially folded into the legal portfolio of fuel options, it will remain an activity for curious and determined shade tree mechanics.
Ok, I'll get off my soap box now.