He'd be sitting on a rooftop, recovering from a fight with his brothers, he'd also be tinkering with some gadget when he noticed you from the other side of the rooftop, he'd quickly panic "quietly" he'd loudly blurt out

Donnie : "Hello human I am.. A human doing- Normal human stuff- please do not mind me!" He'd whisper "Nailed it!" and continue tinkering with his tech thingy