You can wear any pair of jeans that you have at home for a Raj costume, but he does seem to like olive green ones so if you want an excuse to buy a pair then check out the one's featured opposite.
Combine the jeans with a short sleeved business shirt, in either off white or a striped design and then don't forget the sweater vest. I always used to think these sweater vests were reserved for granddads so if you've got a granddad who wears them then you might want to borrow one off of them, if not I've included one opposite for you.
Raj has a collection of different patterned sweater vests and also wears plain ones too, the patterned ones are the ones that really stay in your memory though - aren't they?
Top this combination with a purple zipped sweatshirt or casual jacket and you're nearly finished!
A red cap that just shouldn't be worn with purple is a classic Raj touch, his does appear to have a logo on it, but I'm not sure what it says and when it comes to fancy dress you can take liberties so I've included a 'Life is Good' logo because if you can watch the Big Bang Theory life is pretty good!
When it comes to footwear I don't think you can go wrong with a pair of converse sneakers for Raj, or in fact for any of the BBT geeks for that matter.
Another thing about Raj is his black watch, this always reminds me of the cheap watches you can get at gas stations so would be an extra little accessory to complete your costume. Now you can act shy until you have enough to drink to really be obnoxious and then it's job done - you're Dr Raj Koothrappali!