Someone who purposefully kills conversations.
Someone who repeatedly accidentally kills conversations.
Someone who, by their mere presence, can ruin a conversation.
Someone who has trouble holding a conversation for more than a few minutes.

Essentially, a conversational grim reaper.

Can be shortened to "veeper," though that is even further from the original phrase.
"I was talking to my friends about this random mole that I saw in my backyard, and this douche John started talking about the mole on his arm. It's not even the same mole!! What a fucking conveeper. We just stopped talking and glared at him until he went away."
"I can never seem to keep my conversations going. I'm socially retarded! I'll be a conveeper for life."
by Charles G September 2, 2007
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