Funny / Who Do You Think You Are?
Predictably Jeremy Clarkson's has a few of them. He learns that the vast majority of his family were common labourers who lived around Tickhill for centuries intermarrying with other locals:
Clarkson: I'm amazed I don't have only one eye, and gills.
He later visits Tickhill and greets everyone in the street as though they are close relatives, including a dog.
After he finds out who owns the copyright for the Kilner Jar invented by his ancestor, and goes to meet him:
Clarkson: Now, is he going to give me my millions, or am I going to have to punch him in the face?
Jeremy Paxman has a couple, too: one when he rants at the narrator for asking about his emotional state, and another when he is horrified to learn that one of his ancestors was - a politician!
David Mitchell has many in his episode, ranging from things his ancestors did to waiting forever for an internet connection to work on his laptop so he can do some research...
David Tennant is brought to an old church where part of the floor has been torn up, revealing the remains of people buried underneath it. His reaction? He jumps down and grabs the first skull he sees.
Anyone who thinks Michael Parkinson is a dull old curmudgeon would be amused by the fact that his episode had to be abandoned after the the producers failed to discover anything remotely interesting about his ancestors.