Board Thread:General Discussion/@comment-37042304-20180929043616/@comment-32182236-20180929114703

It's not Sans. "Those pathetic people that want to see it, but are too weak to do it themselves"

Sans doesn't want to see it, and he's too "weak" (actually lazy) to STOP the genocide, not to do it!

Also, Flowey knows that Sans can get serious if pushed far enough.

"If I have ONE piece of advice for you... DON'T. Let his brother. Find out ANYTHING about you. He'll... well... Let's just say.. He's caused me more than my fair share of resets."

So no, that line isn't referencing Sans. The most likely Undertale character Flowey could be talking about is the narrator.