Trump's tweet was a clip from later in the episode. Larry is driving somewhere and cuts off some big biker on a motorcycle. The guy on the motorcycle starts cussing and threatening Larry for his mild driving faux pas. They stop alongside each other at the next red light and it looks like this guy on the hog is going to kick Larry's ass. Larry reaches down, pulls out his MAGA hat, and the guy immediately calms down, telling Larry to just drive more carefully next time.
The joke here is that this scumbag on the motorcycle—a guy who would intimidate, threaten, and possibly even kick the shit out of a stranger for a harmless mistake is a Trump supporter. And because Larry is perceived as a Trump supporter, hog guy will leave him alone—further implying that motorcycle guy would have continued to escalate the situation against a non-MAGA idiot. Let's be clear, Larry is an asshole, and the guy on the motorcycle is an asshole. It's a scathing indictment of the depravity of Trump supporters and everything MAGA stands for.
But Trump fundamentally didn't understand that joke. He tweeted the clip with the caption: "TOUGH GUYS FOR TRUMP!"