frother
/ˈfrɒθə/noun
1An instrument or substance which causes a liquid to form a froth.
2 Figurative and hyperbolical (usually depreciative ). An excitable person, especially one readily provoked to outrage in defence of a principle or ideology.
Origin
Mid 19th century; earliest use found in Walter Thornbury (1828–1876), author. From froth + -er.