When at a party, chances are, someone will bring out a guitar. A guitar in a party is a magnet that sucks out guitar players from the mass of party-goers.
Typically, the owner of guitar will play a few songs, songs that he (or she) has practised for many hours in the privacy of his own room and is therefore comfortable playing in public. Like moths to the flame, guitar players in room will be drawn to the guitar, motivated by a combination of fascination with live music, but more importantly, positioning themselves for a crack of the guitar after the song is finished.
Guitar etiquette says the person who owns the guitar (Owner) must share the guitar with the other players (Guest).
"Wanna play?" asks Owner to Guest. Guest can accept or decline. Here are the rules.
If Guest is significantly inferior to Owner, Guest must decline the invitation.
If Guest feels on a par with the Owner, then Guest can accept the invitation and play one song. Then what follows will be an alternation between Guest and Owner, as they "trade" favourite songs, licks, and tricks, wowing the audience (hopefully) in the process.
If Guest is better than Owner then Guest is allowed to play several songs in a row, demonstrating Guest's superiority. Owner will then say, "Can you show me a few tricks," to which Guest is obliged to show at least one trick that Owner can learn. Then Guest owns the guitar for the rest of the night.
But if Guest is many times better than Owner, Guest will generally decline invitation to play.
Because, after all, when Owner asks "wanna play?", Owner is really asking "are you better than me?"