Usually used in situations where fucking around is not permitted. Hardcore "non-fuckers" will often let people know of their "fucking" status by constantly letting them know by saying "Yo, I'm not fucking around here." They might even apply it to specific examples such as, "I was most definitely not fucking around on that test." People who do fuck around are often looked down upon, unless they can justify the act of fucking around that they were doing, are doing, or are planning to do. A few examples of the justification of fucking around are: if it is the first day of a month (especially if that day is a friday), if it's raining on Boston on the day the fucking around is occurring, if physical education is taking place on that day. Justifications must be completely outlandish, but they also must be said with a completely serious face or else you will have been caught fucking around and further ridiculed for doing so.
Yo Bazin, how'd you do in that game yesterday?
I scored like four goals. I don't fuck around man.