Yeah we are all supposed to be happy, cheerful and inspirational, at all times.
The thing is the grumpy arsehole walking about on legs is not memorable, they are common place, every day, the norm.
The grumpy arsehole on wheels IS memorable, particularly if you thought you were doing something nice and then you got snapped at by them.
We have all the same issues everyone else has that might make us short tempered or snappy.
And then we have the extra bonus shit that comes with being disabled.
Pain.
Judgement - are they just lazy, are they a scrounger, I bet they sit at home on benefits, maybe they are faking it, why aren't they in the Paralympics....
Many things are harder.
Many things are more expensive.
Stress - try juggling multiple hospital appointments and a job, because it is generally assumed we don't work, and have hours and hours to waste being faffed around...
The assumption we SHOULD be happy.
The assumption we are brave, inspirational, etc.
It does get a bit wearing, and there are times when people have I am sure, thought they were being helpful but in fact weren't, and I simply haven't the energy to say 'no thats actually not helpful, I am very sorry that it isn't helpful, but you could stop trying to do that because.. and I am extremely sorry I have hurt your feelings...'
I don't see why its so hard to simply ask 'would you like help, HOW can I help you?'
If the answer is no, fine. If the answer is a rude no, then clearly that person has issues, maybe they have had a shitty day, maybe they are just a total wankpuffin, either way thats their issue not yours.
Helping without asking though, can come across really fucking patronising and if you have had a billionty people that day, ALL assume you can't do something you actually can do easily, and often more easily on your own than with help... I do get why folk might get a bit stropped off with it!