5. 1:2. Adam ki yakriv. Rashi brings from Beitzah 20 that just as the korbanos of Adam Harishon belonged to him-- they were not stolen from others, you too may bring korbanos only if they are yours, and a korban is fatally deficient unless your ownership of the animal is beyond any legal doubt.
Dr. Zvi K suggested an additional interpretation for the connection to Adam. Some people do mitzvos in a special or public fashion because they want to impress other people. For example, some people are very particular about hidur mitzvah when other people can see it: When they buy a lulav and esrog, or a Megillah, they are very makpid in hidur, but when they buy tzitzis, they don’t spend the time or money to be makpid in hiddur. Some people only daven a long shmoneh esrei when there are people watching. (Two points— spending more for hiddur to show off, and doing mitzvos in a showy way to make people think you are a kadosh. Dr. Krinsky was talking about yuhara; the same idea applies to hiddur mitzvah.) We should learn from the korbanos of Adam to be mehadeir mitzvos not to impress people— there were no people for Adam to impress— but rather because of our love and respect for the mitzvah itself, or as a way of becoming kadosh. Do the mitzvah lesheim mitzvah, not lesheim showing off, or showing how holy you are.
This brings up the Gemora in Shabbos 133b, Sukah 11b, and Nozir 2b, where it says “hisna’eh lefanav bemitzvos,” which literally means ‘beautify yourself with mitzvos’. Avromi Isenberg, our generation's Dean of Dikduk, says that the use of ‘hispo’eil’ doesn’t mean anything, just as “ke’ilu hiskabalti” (meaning that I view a monetary obligation as being ended just as if I had recieved payment) means nothing other than ‘ke’ilu kibalti’. But the Gemora in Nozir says that they brought their sifrei Torah to show other people their beauty. The Gemora makes it absolutely clear that the reason they brought them was to show them off. This indicates that ‘hisno’eh’ is meant literally.
Maybe there’s nothing wrong with preening or being showy by beautifying a mitzvah that you are doing. Mechzi keyuhara is, of course, a terrible thing. But perhaps that’s only where you are sanctimonious, where you act in a misleading way to fool people into thinking you’re on a higher madreigah than you actually are, because people will emulate you in your other foolish behavior, or because if you later do something bad it will be a chillul Hashem. But showing off how much you spend on a mitzvah, and that your esrog is the nicest one in shul, is not necessarily so bad— it’s not a lie, and it may even foster the other people’s chavivus mitzvos.
My son, Moshe said that the person is only showing off with it because it is something he cares about. If he was indifferent to the mitzvah, he wouldn’t think it worth showing off with. While it may not be a refined middah tovah, it is a middah tovah anyway, and the benefits far outweigh the detriment. Anyway, think of it like jewelry— “mitzva jewelry”. Although it may be that the main purpose of jewelry and fashion is to show off to other people, and this seems like an ignoble middah, the fact remains that people do wear jewelry and expensive ties, and this is considered normal behavior. So why shouldn’t our tashmishei mitzvah be our jewelry? This is somewhat similar to making feasts, which appeal to our desire for good food, for seudos mitzvah. The same way that the satisfaction of our desire for food, when used lesheim mitzvah, is good, so too satisfaction of the desire to be envied can be used lesheim mitzvah.
The following was added later than the original post.
The Wall Street Journal had a De Gustibus column on March 23, 2007, by Joseph Rago. He talked about Veblen’s 1899 “Theory of the Leisure Class,” in which he introduced the idea of conspicuous consumption, defined as “specialized consumption of goods as an evidence of pecuniary strength.” This is, of course, specific to the “expenditure of superfluities.” The author of the column updated Veblen’s essay to extend to “conspicuous virtue.” People buy more expensive things that are free trade, renewable, cage free, and live strong bracelets, partly, and allegedly, because they want to support the causes these things represent, but to a great degree because they want to proclaim their virtue. (He suggests that this trend has become popular partly because of guilty consciences about consumerism and materialism.)
This is a very nice way of describing the ‘hisno’eh’ attitude: conspicuous virtue, where the motive is partly appreciation for the underlying mitzvah, but also to proclaim your virtue. In any case, the idea I said above is still true: there is a mixed motivation, but ultimately it stems from pride in ability to fulfil the mitzvah.