Even if you don't outright dislike the disabled in that case, that still means you're being inconsiderate of them, which is still a dick move.
That matter is also not that easy

Am I a dick if I forget things which do not directly affect me?
e.g. a few standard settings in scientific tools produce graphs in red and green, red for down, green for up. Many people use them. Many people do not think about the choice of colour. The choice is also rather obvious, since we are used to associate green with positive, and red with negative. Traffic lights and so on. Who thinks of the 2% of people who are red/green blind? Is everyone who ever made a picture in red/green a dick? Or are they just minding their own bussiness?
Are you living in a single family house? How many of them have elevators? Is everyone a dick who ever built a house without an elevator? What about your private tree house when you were a kid? Didn't have one either.
Living your normal life doesn't make you a dick (under the assumption that your normal life doesn't include kicking puppies, spitting on homeless people and insulting minorities).
Your reaction when confronted with a relevant situation (not crazy bat feces, like if the world congress of wheel chair users wants to rent your tree house), that will tell if you're a dick or not (as Traitorfish already pointed out).
EDIT: Let's also add a legitimate rant here:
I have tomorrow a meeting. At 7:30 PM, because we're collaborating with the US east coast, and someone there cannot earlier.
Goddamnit

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