Here are some other ways to say "boring" in Spanish:
* Aburrido/a: (adjective) boring, dull
* Monótono/a: (adjective) monotonous, repetitive
* Insulso/a: (adjective) tasteless, bland (can be used figuratively for boring)
* Tedioso/a: (adjective) tedious, tiresome
* Soso/a: (adjective) dull, bland
* Pesado/a: (adjective) heavy, boring (can be used for a person who is boring to be around)
For example:
* ¡Qué aburrido es este libro! (How boring this book is!)
* La película me pareció muy aburrida. (The movie seemed very boring to me.)
* El profesor es muy aburrido. (The professor is very boring.)