The reason it is ironic is that while in English the pro-Palestinian crowd says it is a symbol of "unity and struggle," in Arabic it is all about "resistance" - which means terror.
It originally was used during the 1936 Arab riots to hide from the British, and then became popular again when Yassir Arafat wore it everywhere. But Arabs understand it as a symbol of terrorism.
This poem, illustrated with the face of a girl wearing the keffiyeh, ends off with "The way to Palestine is through the barrel of a gun."
Anyone who tells you that the keffiyeh is a peaceful symbol of unity is lying, and probably knowingly so.