Pucker = asshole. An asshole will often tighten up- or pucker up - when something important happens. Any event, good or bad, business or pleasure can cause one's asshole to pucker. When my asshole is all puckered up, it is closed real tight - like a fortress.

source: http://www.urbandictionary.com/defi...?term=pucker+up

底下還有更多解釋，這個應該比較符合吉他大看到的吧，參考就好...