Soapbox

soap·box
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
To engage in impromptu or nonofficial public speaking, often flamboyantly.
Idiom:on (one’s) soapbox
Speaking one’s views passionately or self-importantly.