To add another 2 cents to this fairly excruciating topic:
As has been said a few times already in this thread, tipping is the same as a gratuity and gratuity is defined as:
'A reward, service, or payment provided freely, without obligation; An additional charge placed for services rendered' ref: wiktionary.org
Note, 'Without Obligation', so while it is obviously nice to give or get a tip for a service rendered, it is not a requirement.
Given that statement, should someone be called cheap for not tipping? Absolutely not! It is their decision not to tip for any number of given reasons, from the fact they can't afford it this week, or that they don't believe that the service was good enough. You do not know someone's personal situation, making sweeping generalizations is not constructive to any argument.
I'm fairly sure that given all the money in the world and a service that is beyond what is expected, the majority reading this would tip. However, should someone receive a tip for just completing a job that is required of them? No, not necessarily.
People are arguing the side of the van driver, saying that they don't get paid a lot or about how its a retirement job for them. Then also saying that pilots should find another job if they cannot afford to give a tip. Given this reasoning shouldn't a van driver, who knows his basic wage and that he might be given tips, get another job if he doesn't want to do it for the basic wage as he might not be given a tip. Is it the responsibility of a pilot or FA to supplement the wages of a van driver, which he signed up for?
First year FO's are living a hard life given the probable debts they have for school/flight training. Therefore, should not be judged in a topic such as this. They are working hard for the pittance they earn. All in a good cause to provide themselves with a stable (maybe) and lucrative career in the long run. Whatever stage you are in your career, leave them be when it comes to tipping.
In my slightly warped opinion of things, tips should be given for good service, and often service is not good. Now do we define good service as 'service that is required or better' or bad service as 'service that is normal or worse'? There is a huge distinction here and that is down to personal preference. I personally believe that required service is OK and good service is anything better and will tip accordingly.
Given the above diatribe, my personal stance is that I will tip if I can and not if I can't, that doesn't make me cheap, just on a tight budget; it certainly doesn't relate to how much my van driver needs it. How good/bad they were and the number of dollar bills in my limp wallet is much more of a factor.
Given all of the above, I will say that I grew up in a country where tipping is not an everyday part of life, it is rare and for exemplary service, which seems to be rare these days. I have worked a job for tips (skycap) and have lived here long enough to observe and respect the system, this doesn't mean that I agree with it.
Here endeth the dissertation, as you may guess i'm furloughed hence the time to sit and discuss, in depth, the tipping of van drivers on a public forum.
Given my work situation, maybe saving those tips from the last 18 months of work would have allowed an extra $25 per month for food for the next 12 months of unemployment. However, 'life in retrospect is a life not worth living'.