"Doug's Bad Trip". The episode is actually about Doug and his family going on a road trip, but the title suggests...other things.
Surprisingly, in Disney's Doug, the word "sex" is said in the Christmas episode [the one where Doug's baby sister was born, not the Wham Episode where Doug's dog is accused of attacking Beebe at the lake while ice-skating]— the first episodes from the Disney series had a mini-arc where Doug's dad is trying to give his son the sex talk, only for Doug to tell his dad on the Christmas episode that he already knows about it from school. And in another episode, Guy observes a cartoon with donkeys in it by saying "Hmmm, a bunch of jackasses."
Some of the last names sound dirty if you really think about it: Bone, Dink, Buttsavitch, etc.
In the episode where Roger's cat has kittens, he tells his mom that he didn't know the cat was a girl. She replies by telling him that there's a talk that they're long overdue for.
During the Founder's Day Pageant in "Doug's On Stage", look closely; someone in the audience can obviously be seen drinking what appears to be an alcoholic beverage.
There is an episode where Doug makes a funny drawing of his teacher, but accidentally sends it with his essay. The title of the episode: "Doug's Doodle."
While dressing Doug up for his date with Patti, Judy says he should wear a handkerchief, "but not on the left." In the hanky code once used by the gay community, a handkerchief in the left pocket signaled that one was a "top."
In "Doug's Secret Song," while hanging out the second story window of Bebe's house, upon realizing "somebody up there likes me," Skeeter responds with the double-entendre, "yeah, but somebody 'down there' doesn't" (they look down, and Bebe's butler is yelling at them to get down).
The name of Dale's preschool is "Ding Dong Daycare".
Let's not forget about this gem of a line:
Doug: The reason the lava keeps shooting up into the air is because I love you.
In one episode, there is a scene where Doug is holding a banner that said "I (heart) head."
A restaurant at the mall is named "Baloney Hut," and its slogan is, "get your butt to the Baloney Hut."
In one episode, Mr. Bone says "Young man, I want you in my office P.D.Q... whatever that stands for." (It stands for "pretty damn quick.")
It could mean pretty darn quick too.
In the first episode of the Disney series, after Doug's mom makes the announcement of her pregnancy, Judy gives a thumbs up and says, "Way to go, Dad." leaving Doug confused while his dad embarrassingly explains that it's nothing.
Doug's Dad was in a psychedelic band. Let that sink in.
That doesn't necessarily mean it's drug related. Plenty of other children's shows like Recess, The Angry Beavers, and Rugrats have showed hippie music and imagery without any references or other stuff to get past the radar.
In "Doug's Lost Weekend," Doug refers to the aliens in a video game as "nutsuckers."
In "Doug's Brainy Buddy," Skeeter decides not to go to college because all the students smoke.