To not take something seriously, believing the whole thing to be just a joke. It can also be used to describe not putting your full effort into something.
Example 1:
Teacher: All you do is fuck around in my class and break the rules. Don't blame me for your shitty grade.
Example 2:
Person 1: That same fucking cop arrested me again!
Person 2: Well then don't piss him off. I know that guy, and he doesn't fuck around.
Me: Are you getting drunk tonight?
You: Nah I have to get up early tomorrow
Me: That'snever stopped you before
You: You're right. Fuck it in the Bucket
" man you didnt do to well that time"
"Well fuck me sideways with a lunchbox, i made it to the last level man."
"Finally, I would like to comment on an unlikely topic, my pass coverage ratings. I see that I am a better at man-to-man coverage (31) than zone (21). Fuck me sideways with a lunchbox. Where did these scores even come from?" -- Ethan Albright to John Madden regarding him beong the lowest rated player in madden.