In the episode "Microbots", the Decepticons act like they're drunk after "overenergizing" on energon.
In the episode "Only Human", where Rodimus Prime, Arcee, Ultra Magnus and Springer have their minds placed in synthoid human bodies. Rodimus has (offscreen but implied) sex with a human woman named Michelle, the moll of the episode's villain Victor Drath.
"Starscream's Ghost" has, as TFWiki so eloquently puts it, Octane looking up robo-porn.
"The Search for Alpha Trion" has a...questionable...scene where Optimus connects himself to Elita-1 (essentially his girlfiend) to "transfer his energy" to her, and then moans in the process. That's some transfer alright.
The "Hojoni" movie poster seen in the episode "Kremzeek!" depicts a naked woman covering herself.
The second part of "The Return of Optimus Prime" features use of Stan Bush's song "The Touch" from the movie, with the lyric "When all hell's breaking lose" not being removed or altered in any way.
The episode "Roll for it" has a Japanese message by the staff working on the episode, with it roughly translating to "Gah, I need a woman. Ain't there any hot babes around? Let's call it a day, get home quick and hit the sack. Hey, Habara, did you pop your cherry yet?note lost your virginity Let's go hit a Turkish bathnote a kind of brothel some time".