in. fucking around; messing around. (See also fuck around. Usually objectionable.)
They were F-ing around with the switch, and turned it on accidentally.
effing around
rude slang Engaging in aimless recreation or frivolous time-wasting; fooling around. "Eff" is a euphemism for "fuck." I can't believe we spent the whole day just effing around online.
effing around
and F-ing around
in. fucking around; messing around. (see also fuck around. Usually objectionable.) They were F-ing around with the switch and turned it on accidentally.