Doing absolutely nothing productive. Wasting time. Not taking a task seriously. Purposefully performing a task poorly.

syn: dicking around, doing jack shit, chilling
ant: trying, working

Got the covid-19 vaccine

something one does in his/her notice period after resigning from current job, basically nothing.

Messing with someone with no intentions of being together, only for temporary satisfaction.

Not at all engaged in nothing productive. Though it may appear to an observer that the subject is doing nothing or thinly disguising his or her apparent idleness with misleading activity, the subject may be more open to the discovery of something new than if he/she was not fucking around.
Hence, fucking around may be a modest term for continuous searching, remaining open to any and all fresh input.
Fucking around may be experimentation in its noblest form.

Wasting time and being annoying.

Cheating on someone, usually said in bitterness or anger.
Not just kissing, but more. See def 1 for 'fooling around'.
Oftentimes 'fucking around with' or fucking around on'.