When a person no one likes enters a conversation, therefore making it awkward, a douche grenade has been dropped. Named because the person's comments affect everyone in the group, like shrapnel from a grenade.
Bob: Did you see Shaun White's Double McTwist last night?
Mark: Yeah, man. That shit was nasty.
Tom (Friend no one likes): Yo, Louie Vito's better, he just had a rough night yesterday.