Continuity mistake: In the beginning of the movie when the guardians are getting ready to fight off an inter-dimensional being Rocket winks a couple of times at Starlord. Starlord then responds but is looking to his left at Rocket, whilst Rocket is on his right side. The scene is for no reason mirrored, proven by the big orange device behind him also switching from being on his left to on his right.
Plot hole: When Baby Groot finds and brings items thinking they are what Yondu wants, he brings a desk that screeches when he drags it. There is no way he could have dragged it any great distance without alerting anyone, including the guards (seen later) posted nearby. Or if he were closer, Yondu or Rocket would have stopped him. Or even put it back (it's not seen again).
Ego: After all these years I found you. My name is Ego, and I'm your dad, Peter. I wanted to experience what it was to be human. So I created what I thought a biological being would be like.
Drax: Did you make a penis?
Peter Quill: Shut up!
Ego: Yes, Drax, I got a penis. It's not half bad, either.