Scroll down below the infographic for some context -- and watch for a fresh edition of our Twitter Week in Review each Friday.
- When it comes to Twitter, is Lady Gaga the new Justin Bieber? Last month she became the first person to surpass the 20-million-follower mark -- as of this writing she's up to 22 ,294,199 followers -- whereas poor Justin Bieber has to make do with a mere 19,589,931. With that kind of footprint in the Twittersphere, it's no surprise that Gaga, who took our No. 1 spot last week, repeats with the "Happy Birthday Lady Gaga" trending topic. Also relevant is a quirk of timing: Gaga's birthday was March 28, the pivot point between last week's chart and this week's. Given Gaga's global fanbase, which spans most time zones and the International Date Line, tons of people were still wishing her a Happy Birthday when it wasn't technically still her birthday anymore.
- Wonderbra scored a win with its No. 2 showing for National Cleavage Day -- the fake holiday it created in 2008 and that fell on March 30 this year.
- "Happy Birthday Pattie"? Who the hell is Pattie? Well, if you don't know you're clearly not 11. Pattie is Justin Bieber's mama! Her birthday was April 2.
- Dunkin' Donuts kind of scores a place on our chart (at No. 6), indirectly. Via @dunkindonuts it ran a trivia game this week, and one of the correct answers was Ron Burgundy, the main character from the Will Ferrell classic "Anchorman: The Legend of Ron Burgundy." That got people reminiscing about the film and quoting favorite lines. Added fuel for "Ron Burgundy" as a trending topic: Ferrell announced on "Conan" last week that an "Anchorman" sequel is in the works.
- For trend definitions in our Top 10 not covered above, visit What the Trend.
- Our Top 5 Memes chart is topped by #20thingsilove -- and as of this moment the top search result Twitter returns for that meme is : @Patrick_Viloria's " #20ThingsILove Lip Biting, neck kissing, cuddling, Etc <3." (Duly noted!) And Instagram tops our Top 5 Brands chart thanks to the release (finally!) of an Android version of the popular iPhone app.
As with our Top 10 list, you can find more details about our Top 5 Memes and Top 5 Brands at What the Trend.
Simon Dumenco is the "Media Guy" media columnist for Advertising Age. Follow him on Twitter @simondumenco.
Help HootSuite's What the Trend define trends by following WTT: Define Now (@whatthetrend). And stay up-to-date on the latest HootSuite product-update details and company news by following @hootsuite.