I feel like talking about rarepairs vs crackships, since I’ve seen people respond to posts about rarepairs by calling them crackships
Rarepairs are ships which are really unpopular in a fandom, often non-canon but not always! This unpopularity may be for any reason, but it’s mainly because:
-The characters involved are already in popular canon ships
-They don’t interact much, if not at all
-They are side characters
Crackships are things people ship mainly as a funny joke! Often this can be with characters that are from different fandoms, or any other ridiculous or silly pairing.
The main difference is that rarepairs are serious, crackships are not! If a ship seems silly or strange to you, it does not automatically make it a crackship!