soap·box 
(sōpbŏks′)
(sōpbŏks′)n.
1. A carton in which soap is packed.
2. A temporary platform used while making an impromptu or nonofficial public speech.
intr.v. soap·boxed, soap·box·ing, soap·box·es
Informal
Idiom: Informal
To engage in impromptu or nonofficial public speaking, often flamboyantly.
on (one's) soapbox
Speaking one's views passionately or self-importantly.