Season 8 Episode 18 episode 18 How I Met Your Mother Season 8 Episode 18 "Weekend At Barney's" Photos! 02.16.2013. @ 05:02 ShahbazMalik New spoiler-filled photos have emerged for How I Met Your Mother, season 8 episode 18 'Weekend At Barney's". Check them out below. image gallery View: thumbs list Source: CBS , Seat42f Read the official guide for more spoilers! The episode is set to air Monday, February 25th.