Wouldn’t hurt a fly = totally harmless and would never hurt anyone.
- You needn’t to be afraid of him. He wouldn’t hurt a fly.
Give someone free rein = give someone complete freedom.( reins are what you hold in your hands to control a horse when riding)
- They’ve given me free rein to do whatever I like in this new job.
Make a beeline for = go quickly and directly to.
- As soon the meeting was over, we all made a beeline for the food.