Stronger/More Intense:
* Exasperating: Causes great annoyance or frustration.
* Infuriating: Makes someone extremely angry.
* Aggravating: Makes something worse or more annoying.
* Provoking: Likely to cause anger or a strong reaction.
* Vexing: Causing annoyance, worry, or distress.
* Enraging: Making someone extremely angry.
More Informal:
* Bothering: Annoying or causing concern.
* Pestering: Repeatedly annoying someone.
* Nuisance: Something annoying or troublesome.
* Trying: Annoying or frustrating.
More Specific:
* Scathing: Severely critical and hurtful.
* Galling: Extremely annoying and humiliating.
* Incendiary: Likely to cause anger or violence.
The best word to use depends on the context and the specific emotion you want to convey.