dog officer walking into the telephone pole reminds me of the japanese saying 犬も歩けば棒に当たる. literally it means "if a dog walks it'll hit a pole/stick". metaphorically it means that if you start doing something, it'll result in something unexpected. the unexpected thing could be positive or negative, so the saying's meaning is different based on implied context. you weren't doing anything much but you got lucky, or you were being reckless and something you ignored or didn't account for came back to hurt you.
dog officer got full of himself and didn't watch where he was going, so the latter negative meaning probably applies here. to me, the joke is that who he is and what he did lines up with a metaphor that could be used to describe how silly hes being, and the metaphor also happens to literally describe the situation itself.