I am a graduate student at the moment and sharing a house with undergraduate students. What I've noticed is that a lot of undergraduate students who are studying let's say relatively soft subjects seem to have a lot of free time and seem to want to have long conversations with me when I am walking about the house or preparing something to eat.
Unfortunately I am extremely busy with the research project which I am working on so I don't really have time to be having these conversations. Question is: is there some tactful standard way which other people have found useful that I can excuse myself without making it too obvious that I am trying to 'escape' from their conversation or without sounding like a douchebag?