to avoid someone if they are constantly bugging u to do soemthing whihc u dont want ot do or are constantly phoning u to prod for info onur life which u do not want ot igive..say it is an old friend who u havent been around for a while..
if so would you not feel a bit nervous/guilty if htey know ur avoiding them on purpose?
"I dont feel comfortable talking about this with you and thats why Ive been avoiding the topic...Im sorry but this is just not something I want to discuss".
Go and talk to that person directly and tell them I am not comfortable with their behavior. It is always better to settle things straight, avoiding someone never solves any problems.