With accent marks:
Дурно́й приме́р зарази́телен.
A bad example is contagious.
Bad habits and wrong views of one person very often “stick” to other people.
The proverb is used to talk about a person who, without any thinking and hesitation, adopts bad habits of others.
Other Russian proverbs
Strike the iron while it's hot.
Better to see once than hear a hundred times.
If I knew where I would fall, I would lay some straw there.
The forbidden fruit is sweet.
All is well that ends well.
There is no smoke without fire.
A bird is visible by its flight.
What goes around comes around.