It's the maximum expression for describing someone's annoying behaviour.
* bord: annoying, rude, jerk. [see more definitions]
The play on words comes from the fact that in Valencian the word bord has 2 meanings: one is wild, like a wild plant, that is useless and annoying for the farmer. Thus, the sentence would be: To be wilder than a mass of reeds. The second meaning of the word bord is nasty or jerk, as when somebody gets stroppy. The expression is playing with the two meanings, as both (a wild plant and a nasty person) are unpleasant.