Not extremely lazy in the sense that he does work when he has to, lazy in the sense that he always skips out on labor when there is to be division of it.

We work in a museum so he will take groups when it is on his shift (naturally I will always take groups on mine). Thing is when we are both on the same shift he will plant himself firmly in the innermost seat and keep verbally pushing groups to me.

I don't usually mind (I like the presentation experience) but today I was in the middle of processing something important and he kept insisting I take the group till I lost my train of thought and it really messed me up.

I don't want to go to the manager over something so trivial (and honestly I like the extra presentation experience anyway) but I don't want him to interrupt me while again while I'm mulling important decisions, on account of his laziness.

What should I do to handle this in a future repeat incident?