When chatting to the Goth girls, Howard mentions that in space no-one can hear you scream, quoting the tag-line of Alien (1979). In The Decoupling Fluctuation, Howard spends nine minutes screaming continuously on the International Space Station as a result of a practical joke played on him.
When Leonard says what show they are watching its called Oshikuru: Demon Samurai, the title of that show got its name from Charlie in Two and A Half Men as a jingle for a kids tv show in the episode The Salmon Under My Sweater (2004)
Wolowitz presents "tattoo sleeves" as wearable sleeves with printed tattoo patterns on them. Tattoo sleeves are actually so named because, as a large tattoo or a collection of smaller tattoos that cover the entire arm, they resemble the sleeve of long-sleeve shirt.
Confusingly, the fake tattoo sleeves as described by Howard are actually real genuine products, not just the more commonly known term for arm length real tattoos. Howard and Raj are wearing a version described as "realistic nylon mesh tattoo sleeves used in the movie and television industry", similar to ladies stockings.