I have pain on the outside of the wrist when twisting it like a corkscrew (in either direction). tendonitis?

Possible: Tendinitis is a possibility. Overuse is another option. If no history of trauma or a visible bump (ganglion cyst), then the two options described are most likely ones. Recommend avoid offending activities. Using a wrist splint may help rest the painful spot. Anti-inflammatory meds - ibuprofen/naproxe, topical rubs voltaren/flector patch may be tried. Icing should help as well.

Tendinitis: Likely. Use a ace-band pressure helps with stability.