1 If your act is going badly, turn it into a slapstick routine.
2 Offer your visitors a drink.
3 Cousins look exactly alike.
4 Before you hatch a plan, get into a huddle and mumble. Someone should be a lookout.
5 Never take care of your friend's pet.
6 It's not what you think.
7 The cool character is really very lonely
8 Nazis and Romans had British accents.
9 Your third guess is right (see Law & Order, House, CSI)
10 Between 1960 and 1970, everyone was widowed.