Like, once every few sentences. I say "forgetin.." instead of "uhh" a lot. "I ate like.. forgetin.. three hours ago?" I also just casually say "monday" every time anything doesn't go the way I wanted it to / expected it to. So when I play video games and die I say monday a lot. Aside from that it's just part of my vocabulary, "what the forget is that guy doing," "wheres my forgetin' car keys," "what the forget?", "damn, I'm hungry," etc.
I've never lost a friend or anything because of it though, I've never actually had someone get sensitive about it except when I use the word "handicap." When people get all social justice defender about the word handicap I simply tell them they're a handicap and promptly turn away since that usually shuts them up.
