I get quite a lot of "feedback" from women about the length of my nails. I do not give excuses - they are my nails and I can have them as long as I like. Having said that, it is actually true that I use them for picking up small objects and I use my thumbnail as a tool - I just don't share this. It is also true that I hate cutting my nails and toenails and do so only when they become unbearable. When I was getting pedicures regularly (for about five years the only time I saw my natural toenails was at the beauty salon) the best bit was having someone else do the horrible job of trimming my toenails.
Partly the cross-dressing has identified good ways of living that make sense independently of the cross-dressing, like shaving underarms. So the excuses do actually make sense on their own. I just won't use them as excuses because I do not feel the need to excuse my cross-dressing.
If you like wearing particular clothes and you look good in them, what is your excuse for NOT wearing them? Only society. I have to admit I am careful where I wear womenswear in public, whether it is as a man in a skirt or fully dressed. I would rather be thought of as a crossdresser than a liar. You could go for the double-bluff to avoid lying by saying the skirt is from your vast skirt wardrobe, or claim assertively that you are getting in touch with your feminine side - but you HAVE to assertive about this or they will believe you! Or you can go on the counter-attack (possibly you need even more confidence for this one) - "Do my long nails disturb you? Why do you think that is? or So why is it exactly you find my underwear an issue? And fix them with a scary stare.
All of this is of course so much easier of you don't have a partner who disapproves.