The concept of indexicality is a wide ranging one, but many facets of this phenomenon are recognizable to non-specialists. One facet is the way that certain kinds of language are understood to point to (or be indexical of) certain kinds of people. Today’s media on indexicality comes from Friends.
The way we use language inevitably gets read to mean that we are a certain kind of person: cool, or old, or like a scientist, or like a Canadian, or like doge, whatever. There’s no one iron-clad set of rules that could tell you how to sound a certain way: these linkages between talk and person are always embedded in social interaction and are subject to change.
This entry from the show Friends has Joey trying to take advantage of the indexical qualities of some words to make himself sound smart. Because of some very poor guidance from Ross, Joey ultimately fails to get his letter understood as the kind of thing a smart person would write. Unfortunately, poor misled Joey remains the target of the humor here, rather than the ideologies that evaluate language use in order to enforce social hierarchies.