"boo" can refer to a number of things. Check the current list of boo_* tags to see if there is a more specific one that fits what you are trying to tag.

Some of the more popular tags from the list include...

Species

• boo_(mario)
• boo_(sonic)
• boo_(super_mario_sunshine)

Characters

• boo_(boo3)
• boo_(monsters_inc)
• boo_(ketzio_and_gbb)
• boo_(accalia)
• boo_(artist)
• boo_(baldur's_gate)

Artists

• boo_be_drawing
• boo_(artist)

...but check the complete list if the one you want isn't listed here.

At the time of writing (2022-12), the tag for for the noise that a character makes to either surprise another or express disapproval is under discussion. It may end up being boo_noise, or something else.