Continuity mistake: In the scene in the karaoke shop, watch the light through the window. Sometimes it's daylight outside, sometimes it's dark.
Continuity mistake: In the beginning scene where Brian is telling his sad story to the bartender at the bar, he pulls out a picture of him, Jacob, and Anna. Then the movie progresses to a sequence of their childhood, and then focuses back in on the picture. The two photos are different. One is a close up of the three kids' heads; the other is taken from much farther away.
Continuity mistake: At the end when Ben Stiller is about to talk to the audience about not being honest the clock is first 10 past 7, 15 seconds later it is a quarter to 8.