A chewy, sticky wad of flavored sugar (or sorbitol or xylitol if it's sugar-free, smarty-pants) that may come as a ball, a stick, a cube, a 6-foot strip in a pink plastic dispenser, etc. Typically flavored as either classic bubblegum, a fruit (juicy fruit, strawberry, watermelon, orange, kiwi, pineapple, dragonfruit, etc.), or some kind of mint (peppermint, spearmint, wintergreen, winterfresh, sweetmint, smooth mint, polar ice, fresh mint; the list goes on. What's the difference? Don't ask me.). Common uses include sticking it under desks, putting it in people's hair, playing with it as slime, using it as a currency/bribe, breath freshener, etc.

when you've done something so cringe you can't stop replaying it in your head and it stops you from getting on with your every day life

High School Currency

a bachelor's toothbrush.

something you chew on when your bored in class

A delicious rubber like candy that people chew when they are bored or are hungry for sugar.
Bubblegum is gum you chew and can blow bubbles out of.
Chewing gum can only be chewed, most people chew chewing gum for fresh breath.
Gum has many different flavors.

Most common for bubblegum: Strawberry
Most common for chewing gum: Peppermint

Good thing that people chew. Comes in various flavors and is rubber like.