When "Virus" explains about the monthly income of Rancho Farhan and Raju's parents, the "two" and "five" in the amount written on the board keeps changing shape in every shot.
When Farhan and Raju are threatening to drop Mr. Chanchad's remains down the drain, they drop the pot's cap in the commode but when they hand back the pot to the real Ranchoddas the cap is still there.
One of the first scenes, with Madhavan in an Air India aircraft, shows a distant shot of the aircraft to be an Airbus 321. Though, when moments later when the captain calls for an emergency landing at Delhi, the cockpit is that of a Boeing.
When the librarian Mr. Dubey narrates the speech to Chatur, he begins with this line: "Hamare director Sahab Ne Yahaan Kai Chamatkar Kiye Hain!" In the actual speech this line is missing! And Rancho did not change the speech; he only changed some words and added a Sanskrit Shlok.
Suhas enters through the main gate during the wedding, which is not possible as he was already in the building where the wedding was taking place.
The characters are shown speaking on mobiles near Pangong Tso (about 150Kms ahead of Leh) towards the end of the movie. There is no mobile coverage in the area. The last being at Tangtse (about 100Kms from Leh).
The outside of the plane is shown as a regional airbus a321 But inside it has a business class seating of 2-3-2 as in air India's 777.
Rancho claims that India has no.1 suicide rates which isn't factually correct.
Some consider Pia and Suhas getting back together after 5-6 years a plot hole. However, this is entirely conceivable considering the pressure from both families.
In the beginning of the film, when Farhan Qureshi boards Air India, the aircraft shown is Airbus A-321 series from outside and inside the cabin all is fine. At the time of emergency landing, there is a shot with main landing gear (wheels under the belly) of aircraft, they certainly do not belong to an Airbus 321. They are of a wide body airliner such as a Boeing 777 or Airbus 330. The visible difference between the 'before' and 'after' is simply, clearly seen from the number of wheels.
Obvious dummy baby used in the childbirth scenes during medium shots (close ups show a real baby). Particularly noticeable are the baby's 'rubbery' feet and legs.
During the baby delivery scenes, supposedly taking place around 2003, both parties engaged in the video chat use Google Chrome web browser which was not released until 2008.
Farhan (as narrator) says he was born in 1978. Chatur, presumably about the same age, says (in the hazing scene) that he was born in Uganda, whose dictator Idi Amin (1971-1979) expelled nearly all Indians in 1972.
The mobile phones used in the college period are the ones which were not used in 1998 when the film is set.
During the final scene when Sharman and Madhavan fight with Aamir, the crew is visible in the background.
The airport shown in the start, is actually shot in Bangalore and not Delhi.
Raju and Farhan searched many years for Rancho, but they could have easily checked the college records for Rancho's details. Even Virus knew about Rancho's family background.
Rancho (Aamir Khan) studied for a Mechanical Engineering degree. However, the real Ranchhoddas (Javed Jaffery) gets tenders of Highway Bridge, related to Civil Engineering.
Any professor with any knowledge of space travel would know why pencils were not used in space. It is because the graphite and graphite shavings (to sharpen the pencil) are very dangerous particles in zero gravity.