This is the flag of Chad
This is the flag of Romania
Yes the joke is that these look pretty much identical. The shades of Blue, are admittedly different but well how did this happen??? Alot of countries use a tri-colour design and these are the three primary colours, so there is some sense in which if 2 countries are picking the same flag this might well be it.
Chad adopted it's flag on the 11th of June 1959, and retained in 1960 when independence from France was established. At the time Romania's flag had a coat of arms in the middle, this was changed to another coat of arms in 1965 and finally changed to the current flag on December 27, 1989.
In 2004 there where apparently rumours of Chad bringing this up in the united nations. Then president of Romania Ion Iliescu make a public statement that his country would not give up the flag.