I'm looking at a set of areas in which information acquisition is difficult, and in which choices or decisions have very strongly social implications. These are quite frequently areas in which choice is very strongly ruled by fads or fashions -- strong and often rapid shifts in preferences, but without a long-term persistence -- a winner in any one period will be likely to revert to mean in another (though other influences may sway this).
The areas I've identified:
1. Clothing and fashion -- the practical reasons for distinctions are few, and often counter the popular choices. But these have a very high signalling rate for social status and alignment.
2. Management practices. Here, the problem is that determining actual quality is quite expensive, most especially in time (results may take years, and there's a high noise element to measurement). At the same time, adoption signals group allegiance and has strong carry-on effects with in a market (consulting services, training, education, organisational systems, etc.).
3. Programming languages, tools, operating systems, editors. As with management tools, measurement is hard and takes a long time. At the same time, there are network and lock-in effects which can develop, as well as organisational and market-signalling effects.
4. Food and diets. "Fad diet" is a well-developed concept, going back to the 1960s. The concept of food as a social identifier is much, much older, and can be an element in keeping social groups separate or allowing for their integration. The segregation of Chinese and Muslim populations in Indonesia, for example, derives in part from the affinity for pork by the first and absolute aversion by the second group. That's contrasted to the situation in Thailand, where the Buddhist indigenous population doesn't have a pork aversion and mixes far more freely with the Chinese immigrant elite (from Amy Chua, Harvard scholar and author).
5. Pop music. Beyond a certain base musicality, hit tunes in the 1940s - 2000s were largely a result of both highly focused marketing and some degree of organic development. Experiments with "artificial" hits (within selected group populations) has seen different choices evolve within different groups, from the same base set of songs. Again, music is very highly associated with social identity.
6. Wine. Fads emerge here because it seems so difficult to objectively identify and communicate distinguishing characteristics among different wines. The market offerings are huge, and quite confusing, with information aquisition by individuals difficult and expensive. Choices are very strongly influenced by advertising, marketing, and chance exposure.
There are numerous other goods or behaviours which could be treated similarly. Sports choices, physical fitness training modalities, books (like wine: expensive to judge), etc., etc.