When Adam (Ashton Kutcher) is talking to Lucy (Lake Bell) in his downstairs bedroom, there is a guitar at Adam's back. You can see a reflection of the mic boom in the head of the guitar and it moves down as Adam sits down.
When Wallace takes a picture of Adam and two girls at a party he holds Adam's phone horizontally (landscape orientation). Seconds later the picture received on Emma's phone is seen in vertical layout (portrait).
Adam flinches and turns his head well before Emma slaps him in the emergency room. Not only was the slap unexpected, but Adam had taken painkillers, so he should have been far less likely to react that quickly.
When Emma is carrying the two cups of coffee to the car after running into Adam, she carries them like they are empty, not accounting for the coffee inside. If there was coffee in either one, it would have spilled everywhere.
When Adam (Ashton Kutcher) is talking on the phone trying to find a girl to have sex with, you can see on his iPhone that it is not really on a call. You are able to see buttons that do not appear while talking on the phone.