Why did a coworker accidentally say 'when are we going on vacation?'?

So i have a few male coworkers who goof off all day. Today they were talking about how they could all go on a vacation somewhere. Then this one guy who has in the past repeatedly tried to invite me to go clubbing and go to strip clubs with him said 'lets go--' and corrected himself quickly to say 'so when are you going on vacation?'
Why did a coworker accidentally say 'when are we going on vacation?'?
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