edit: also, I think sometimes preferences are kind of fuzzy. Like, maybe I have no social energy and feel like staying in, so I'll only follow through out of a sense of obligation -- but there's a decent chance the social contact will actually energise me and be enjoyable once I snap out of my funk. So maybe the social pressure is good for me up to a point -- but if my friend is feeling the same as me, maybe we'd both be better off taking the night off and seeing each other next time.
And if you really need to back out because of course nobody is always perfectly estimating their energy levels, you simply say it like it is: I'm tired, let's reschedule for some other time.
Respect is shown by not wasting other peoples time. Don't act, if we are really friends I'll see through you anyway, and I also respect that you really are tired and cannot come.
Do you want to be a flake and do you want others to think of you as a flake? If not, just keep your social commitments. Pretty basic stuff.
We're all human, and we all need downtime, no shame or guilt in admitting that.