First of all I have to say I do not know enough about your situation to offer an advice that I would present as ‘informed’ or ‘thorough’. What I’m about to say, please bear in mind, is no more than personal and subjective advice (which nonetheless I hope it can serve you in some way).
As you said, if the the person were to ask you politely and before acting, it would make a world of difference, wouldn’t it? Basically the person would be paying due respect for your items, your space, and your choices — even if in the end you decided to lend your items anyway. So this is not about the person can use the items or not, it is truly about the attitude of the person, which in this case, it does seem to be in blatant disrespect to you.
In certain situations which are relatively undesired yet mild, it’s okay to ignore, perhaps hoping it’s a one time thing, or that it fades away in time. To do this is a sign of balance and wisdom. Lacking the skill to look the other way when the situation is not that problematic, can lead to a mode of operating where you’re overreacting to everything; you’re dealing with things in extreme ways, with lack of patience or intolerance.
But there are situations where ignoring simply allows the problem to grow and fester beyond your control. It’s like if you spotted harmful weed growing amidst your garden. The best course of action in that situation would not be to ignore it and just let it be there. Because in all likelihood the weed is simply going to spoil your garden and interfere with its health and ability to grow what you want in it. This interferes with your intention for the garden itself. Instead, the best course of action is to proceed to root out the weed.
When a situation interferes with the intention and purpose you yourself defined for a personal space or energy, then that situation is trespassing. It’s in violation of the boundaries and rules you had set. It is akin to the weed that has invaded your garden. It provides zero benefit to it, and it contributes only with harmful effect.
Those who are sensitive can sometimes feel most comfortable in avoiding confrontation, to avoid causing discomfort to others, or for fear of disturbing the harmony of the place they’re in. Perhaps you’re restraining yourself in dealing with the person because he’s not accessible; because you fear the consequences of dealing with this.
But there is a time and place when even that ceases to matter. In other words, whether the person is inaccessible, if he’s not going to react well, or if he might retaliate, will no longer be valid deterrents for you to take action. There comes a time when you no longer let these things censor you. Because your space, the one where you are supposed to have the last saying, is being trespassed. When this time comes, you’ll simply tackle the issue frontally, directly, taking the measures you deem adequate to protect your space.
I see this situation, deep down, as a lesson for you. You’re being asked to learn that there are situations in life where you can apply your ‘regular’ way of dealing with things — a way that attempts to achieve balance, peace, and harmony around you; but then, there are other kinds of situations where that isn’t quite possible, and require a different course of action.
This is what I feel about what you wrote. Hope it helps in some way.