fool around with (something)

to amuse yourself by doing or saying something that is likely to cause trouble.

You don't want kids fooling around with matches.

• a thin skin
• a third wheel
• at home
• a thorn in someone's side
• a thorn in something's side
• a three-ring circus
• a tight-arse
• a tin ear
• a tin god
• at issue
• at knee
• at large
• at last
• at least
• at leisure
• at length
• at liberty
• at loggerheads
• at long last
• at loose ends
• at low ebb
• at most
• at mother's knee
• at no time
• at odds