Trainers » Rare Candy
Could you Rare Candy a Pokémon and NOT play an evolution on it just to get rid of the Rare Candy?
No, you cannot discard a card for free. You must be able to attach the Stage 2 card, or you cannot use the Rare Candy.
Source: PUI Rules Team (2003-10-30), PUI Rules Team (2003-12-04)

Relevant cards

Note: All applicable cards may not be listed below.
BW10_105
BW10_85
BW5_100
DP4_102
EX13_90
EX2_88
EX9_83
HGSS2_82
POP5_7
POP8_10
SM1_129
SM2_165
SM7_142
SWSH1_180
SWSH1_180
XY5_135