That's ok, people are entitled to think what they want, I just wish they wouldn't presume (see update).
Speaking for your employer, they have no choice but to presume. With current HR policies being what they are, after you make it past the probationary period it is extremely difficult to terminate people without having major issues at some point down the road. For myself, if you were to call out on your first week working for me you would have also been fired. This isn't anything against you or what you did in any way and I don't want you to think that. But if you look at it from my perspective a young kid calling out on his first weekend scheduled? On a statistical basis that is about the worst type of employee you can have on your staff.
Now, if you had dragged your @ss in half dead, puking all over the place on your first weekend then you would instantly elevate yourself considerably in my eyes, and without mentioning it to you you would have been put in for a larger post probationary raise and you would have had an ally on your side when issues came up.
Two extremes I know, but that is the reality of today's workplace. The younger generation overall svcks as employees. People say that corporations don't care about their employees but that is rather laughable. If I am about to lose one of my stronger people I make a phone call and a specialist from corporate HR will drive six hours to talk things over with him and try to do what they can to keep him on board. I have had guys get a 15% merit raise off schedule because they were thinking about leaving before- not had given their notice or were actively looking for other employment, just thinking about leaving. Strong employees are a companies greatest assett, and anyone who thinks they don't know that is nuts. This doesn't mean that they should bend over to the half baked demands of some kid who has been working their for six months, but they will work with their strong employees- regardless of age- if they come out well for them.
I understand your perspective on the situation not being pleasant to be in. Next time something like that happens consider it an oppurtunity. Drag yourself in, and in all honesty if a strong amount of appreciation isn't shown to you then that is a place you don't want to work. There are certainly managers out their who don't care about their people- and you don't ever want to work for them. If you work every day as if your life hangs in the balance- you are assured of being extremely successful.
To some of the wet behind the ears kids who think that hard work doesn't get you anywhere- how about up to eight weeks paid vacation per year, nice fat profit sharing checks, stock options and 100% match up to 8% on your 401K to go along with your *free* pension plan? That is what my company offers for our
hourly employees who stick with us and perform exceptionally. Gold watch? Sorry man, you actually don't get one of those. But we have a large number of hourly employees making well above the household median income of the US by themselves(not including spouses) for jobs that require no prior training or educational background. Layoffs are a reality at my business too, we even close down facilities sometimes. When that happens, I personally hand out a partly filled out internal application for my best people and tell them they really want to apply(letting them know without telling them explicitly they have a new position and a raise waiting for them- even if it is a 'lesser' job short term).
I am not a baby boomer, I am GenX. I have a decent portion of my people from my generation and GenY and overall they demonstrate phenomenal work ethic on a daily basis. Of course, this takes time to get to and you have to fire ten or twenty people to find one worth keeping, but when you do you do whatever you can to keep them happy. The OP may have been one of the people I really would have wanted to keep around, but if I see any hint of a problem in the probationary period they are gone. This isn't because I am a knee jerk reactionist by choice, it's just that if I wait then it is a six month to year long process to be able to fire someone.