Entertainment Tonight had an exclusive first clip last night from Britney Spears's seemingly therapeutic stint as a guest star on How I Met Your Mother, which resumes Monday night. In it, Barney (Neal Patrick Harris) uses Britney's obsessive character, Abby, to make his estranged friend Ted "jealous." [videoembed size="full_width" alignment="center"][/videoembed] "Girlfriends are lame! Unless they're me." It is fun to ...