Definitely mention that he went over a solid line, and that he slowed traffic. Have your friend mention that he went into your lane and you made evasive actions to keep from him hitting you. Choose your words carefully when you make your statement. Avoid words that imply you were going fast, or that you hit him. Always say stuff like, "I tried to avoid him colliding with me," or to that effect. Mention you were at the same speed as the guy to your right, who had to suddenly slow down to accommodate this guy, and you weren't able to slow down enough before he illegally merged into your lane.
1997 Pontiac Grand Prix GT, mod list: CAI, more to come...
Sound: Kenwood X889 w/ 800 watt amp. Boston SL95'* rear, SX50'* front.
Appearance: Short antenna, projector headlights, custom grills