Still working through my French words, although this one has a more circuitous evolution.
Pastiche comes from the French "pastiche" meaning "a medley" from the Italian "pasticcio" for both "a medley" and "a pastry cake" as derived from the Latin "pasta" for "paste" and "pastry cake", which took the word "pasta" from the Greek for "porridge or barley". There was a great joke about flour and water makes paste, but add eggs and sugar and you get cake--what happened to the paste? Well, this word evokes the joke. From the paste we get the pastry and then the imitation of the paste and/or the pastry from different pieces, and then just the disparate pieces in imitation of anything. It is certainly an eccentric derivation, but not without a rational thread, even if the evolution is due to lazy usage. What happened between the Latin and the Italian that the word came to mean a medley and not just a food? Was it something having to do with the combination of disparate ingredients of flour and egg to make the pasta that inadvertently came to be a cake and the medley of ingredient to make the cake? It's plausible, but still a little weak. However, as the Italian was arguably coined c. 1750, it is not improbable as the form of the pastry as a sweet was beginning to emerge.
A tart is a conduit for a pastiche of seasonal fruits. I especially love it when the literal the figurative merge. A quilt was originally a pastiche for remnant fabrics. P.D.Q. Bach employs a pastiche of elementary tunes from chop stix to childish taunts in his works. Statutes are a mere pastiche of unedited legal language from countless amendments. Since pastiche carries an element of creativity to the integration of disparate elements, it is typically used with artistic forms (music, cooking, writing). Therefore, although a homeless person's wardrobe may be a pastiche of charitable donations representing various decades of fashion, this may be a bit extreme. The decor of her home represented a pastiche of family heirlooms and curios collected from a myriad of exotic trips. Better. A mutt is not a pastiche of a its genealogy since it has no choice in the artistic make up, but a new breed may be so bred. Since pastiche is inherently artistic, there is an element that the creativity should be deliberate, and not merely by chance. The combination and/or imitation is intentional, and not a mistake in a new recipe or an inadvertent copyright infringement. Plaintiff's counsel's brief read like a pastiche of prior briefs for other clients, including the inadvertent typo of leaving in the other client's name, and therefore, carried no real persuasive effect.