Venn Diagram of Poker Hands:
FOUR OF A KIND and FULL HOUSE are both inside THREE OF A KIND and TWO PAIRS, but do not overlap.
THREE OF A KIND and TWO PAIRS are both inside PAIR.
ROYAL FLUSH is inside STRAIGHT FLUSH.
STRAIGHT FLUSH is inside STRAIGHT and FLUSH.
PAIR, STRAIGHT and FLUSH are all inside HIGH CARD.
Because any hand has a HIGH CARD and HIGH CARD includes all the others, HIGH CARD is identical to ALL HANDS.
The above diagram is topologically correct, I think, so it doesn't really matter what sizes or shapes the boundaries take.
An additional problem, for those who love easy combinatorics, would be to show the numbers and probabilities for all the regions. This requires a slightly different interpretation of the labels: for example, HIGH CARD is interpreted to mean "HIGH CARD ONLY" which excludes PAIR, FLUSH and STRAIGHT.