Words such as “dude,” “man,” and “bro” serve as powerful and popular signals of solidarity, according to linguist Valerie Fridland.
These terms fall into a category of vocatives known as “familiarizers.” Beyond their primary function of grabbing attention, familiarizers are used to impart social nuance and signify a casual relationship. Their utility extends to performing interactional tasks such as signaling closeness or commiseration, expressing or softening disagreement, and facilitating conversational turn-taking.
Fridland points to the different relational messages conveyed by the word "bro" in contrasting phrases: "Bro, you ate my pizza!" versus "I love you too, bro."
Other common vocatives in English include names and nicknames, familial terms like "dad" or "nana," and formal address terms such as "ma’am" or "your honor." Group-directed terms like "hey you guys" or "y’all" are also regularly heard.
A notable observation is the masculine nature of these familiarizers. Terms like "dude," "man," and "bro" are inherently associated with males. This extends to words such as "buddy" and "guy," as well as the British "bruv" and the Australian "mate."