Oil and water don’t mix
Old soldiers never die, they just fade away
Once a thief, always a thief
Once bitten, twice shy
One good turn deserves another
One half of the world does not know how the other half lives
One hand washes the other
One man’s meat is another man’s poison
One might as well be hanged for a sheep as a lamb
One law for the rich and another for the poor
One swallow does not make a summer
One volunteer is worth ten pressed men
One year’s seeding makes seven years weeding
Only fools and horses work
Opportunity never knocks twice at any man’s door
Out of sight, out of mind