It's a metaphor. the "fuck" is metaphorical for not giving a shit, and the "your couch" is metaphorical as it is the subject that the user choses instead of the person it is being used against, thus making it clear that it is more important to the user than the recipient, and by not giving a shit about something that is more important to the user than the recipient, the user is saying that he or she less than gives a shit about about the recipient and anything they have ever said or done
To hijack a partly-completed task from someone else, either directly or via unsolicited advice. Originated in whitewater raft guide culture, and is used most frequently for kitchen tasks.
I didn't mean to fuck your chicken, but you left these tomatoes sitting halfway sliced and I wanted to finish making the sandwiches.
Can I help you do that? I'm an expert at making alphabet-shaped pancakes.
No, I got it. Quit trying to fuck my chicken.