Opposite of 20 Across

• Loser of friends
• Causer of estrangement
• An unpleasant person who causes friendly people to become indifferent or unfriendly or hostile
• Turnoff
• Poor diplomat, say
• One who instills hostility

Wiktionary Word definitions in Wiktionary
n. A person who alienates

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Alienator \Al"ien*a"tor\, n. One who alienates.

WordNet Word definitions in WordNet
n. an unpleasant person who causes friendly people to become indifferent or unfriendly or hostile