Could caffeine use exacerbate osgood schlatter's in teenage boy/and or poor diet?

NO: Osgood schlatter is an apophysitis - irritation to a growth plate in the proximal shin bone (tibia) where the patella tendon inserts. Caffeine plays no role. Most commonly it is aggravated by jumping, running or sprinting- activities that cause pulling on the patella tendon and therefore place stress on this attachment. Sometimes a direct blow to the area will result in pain/swelling.

Unlikely: Osgood schlatters is a problem related to the growth plate at the top of the tibia and usually becomes problematic during periods of rapid growth as the bone growth outpaces the ability of the muscles to grow and stretch. While inactivity and obesity can make it worse, i don't think caffeine would affect it. Generally speaking, though, caffeine intake should be limited in growing children.