be like watching paint dry
To be very dull or boring. Everyone loves that period drama, but, to me, it's like watching paint dry. Rachel fell asleep during the big game because she thinks that watching sports is like watching paint dry.
watching paint dry
If something is like watching paint dry, it is extremely boring. Daytime TV is like watching paint dry, except not as colourful or useful. I replied that cricket was the most boring sport on earth, even worse than watching paint dry.