[s5e17] Of Course -

: Jennifer Lopez’s appearance was highly anticipated and contributed to some of the season's highest ratings. She reportedly improvised several of her sharp, anti-Barney lines.

: Robin admits to Anita that she isn't handling the breakup well. Anita agrees to help by subjecting Barney to her "seventeen 'no's" rule—systematically rejecting his advances to break his spirit.

: Where Robin and Anita first meet and bond over their mutual distaste for Barney's behavior. "How I Met Your Mother" Of Course (TV Episode 2010) - IMDb