Human fire blanket
When someone shows so much as a flicker of excitement about something, the human fire blanket will smother it with a negative comment about how it probably won't work/ he's never liked such and such, etc.
Son: "Dad, I've been thinking about this for a long time, and I've decided to change career and start a landscape gardening business."
Dad, aka Human fire blanket: "There are already too many people doing that."
Dad, aka Human fire blanket: "There are already too many people doing that."