When someone is on the phone, texting or are otherwise occupied whilst their friends are in the same room having a conversation. Much like the common internet meme with the picture of the nerd reading a book while a girl is pressing her tits up against him, there is a caption that reads "GTFO BITCH, IM DOING SCIENCE". In this instance the nerd is doing science
Steve: Hey did you see that band play last night?
Bruce: No, how wehere they?
Steve: they were fucking awesome!
Rob: *off in the corner texting his girlfriend
Bruce: Wow, Rob needs to stop doing science and actually enjoy his friends!
A sexual innuendo for having sex.
"Hey you want to go to my house and do some science?"
"I have to work on learning about science"
"I'm going to be doing science later on..."