Yes, that's Katy Perry in the background of this How I Met Your Mother scene. She guest stars on the show as a woman named Honey.
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Barney opens up to a woman named Honey on the February 7 episode of How I Met Your Mother and... hey, that's Katy Perry!
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Yes, that's singer Katy Perry on How I Met Your Mother. She plays a character named Honey.
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How I Met Your Mother Season 6 Episode 15 Quotes

I'd say hump her brains out, but somebody obviously already has.

Ted

I just had a great TV audition, behind the KFC where the producer works on the weekends. Long story short, I'm going to be on LOST.

Honey