There's surely a pun but I don't get it. It looks like Nazrin is copying a famous song or something but my culture is pretty limited, when it comes to Japanese songs. Here's a fast translation anyway.
Hmm, maybe this is from Yakitatte Ja-pan where there's this contest judge that's a pierrot that keeps making impossible feats and ridiculous decisions, when people all go wtf he just responds with "since I'm a Pierrot~". Of course I could be mistaken about it, since I'm Nazrin.
Seems so, at least TH wikia says so. If it's used in other posts (rather than in comments only), this should probably go to "origins" pool, since I'm Nazrin
Fixed, Since I'm Nazrin.
A THIEF--!Barging in from the roof!I come to steal your precious Chikuwa!Ha!? The Chikuwa!Since I'm Nazrin!Since I'm Nazrin!!