honestly, i do that alot. usually with me it's the 3 months rule of thumb -- if idon't talk to someone for more than 3 months, then i don't need to stay friends with them. i clean out the phone address book quarterly
if you want to be friends, lets be friends. don't just say it and make me keep your IM name and phone number in my contacts so that you can not talk to me.
other than that, when people suck, i just stop talking to them. i never felt the need for any dramatic "fuck you, get out of my life" (though there have been times that would have been fun and appropriate), usually people will get the hint and leave me alone if i stop returning calls, IMS and emails.
on the other hand, sometimes i don't return messages for weeks at a time. oops.