Former President Barack Obama made a suggestive hand gesture while slamming Donald Trump's "weird obsession with crowd sizes" during his speech at the Democratic National Convention on Tuesday.Thomas A. Ferrara/Newsday RM via Getty Images; Adam Gray via Getty ImagesBarack Obama made a suggestive hand gesture while mocking Donald Trump at the DNC on Tuesday.The size joke was a hit with the audience and with many people online.Obama's speechwriter said Obama improvised the visual gag on the spot.Barack Obama's viral joke about GOP nominee Donald Trump at the Democratic National Convention on Tuesday was improvised on the spot, says his speechwriter.The former president dunked on Trump's "weird obsession with crowd sizes" during his speech while drawing his hands together to demonstrate that he was referring to a small size.The visual gag drew laughs from the audience and led some people online to speculate that Obama was cracking a size joke at Trump's expense.Obama on Trump:“This weird obsession with crowd sizes.”