imagine
this is blooky’s response to things they find distressing
considering they find it hard to truly accept praise, compliments, or encouragement,see exhibit A, it is likely these instances are a source of anxiety for them until they can see the person is really being genuine
whenever ghost!Mettaton encouraged, complimented, or praised them, their initial response might’ve been a disbelieving ‘…….oh no………’
and so we have the humble origins of Mettaton’s ‘oHH yeSSSSSSSS’