Very specific examples I have personally witnessed would include:

• People getting angry/irritated when they see young people exiting a car parked on a disabled spot without any obvious impairment or disability.
• People in public spaces (museums, tourist spots, etc.) taking it for granted that if they just saw you climb a few steps, that means you are necessarily able to climb 50 steps without any issues.
• When someone asks if there is a place to sit in a public building/area, staff/officials will often just answer “no, sorry” without considering that the person may actually really need to sit, even if they don’t have a cane or something similar (in which case, they are often much more accommodating)

These are anecdotal, and specific to people I know and their disabilities, but I feel they illustrate how it’s always good to just take a second to think about this sort of thing. It’s also usually a good idea to just ask, instead of assuming.