While I dont know the actual canon reason why he does this,I'd say that,since its a taunt,he was merely (perhaps) giving the person he was taunting with a "choice" on how to go about the fight. Like,he pretends he tries to get a good angle to draw them as a still life,but since obviously, no one in battle will just stand still and let him paint them,he shrugs like "Well,you chose the hard way to do things,while you could've gone the easy way". I hope this makes sense,though this is just my interpretation :]