Jack Applin sends this in. “Bob states that all the sides and angles are equal, which is true for a (regular) octagon. Yes, and … ? Is it a gag about the word “side”, that there’s no need to get to the other side, because all sides are equal?“
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Unless someone can think of a reason why it might be meaningful, let’s assume that “⦣BDC” is simply a typo for “⦣BCD“.
Here are a couple of octagons that are not regular. After someone explains what the joke is, we can consider whether the joke would apply to these octagons.
Comics I Don't Understand 
“Joke” aside for the moment, is that a fetus the flower is talking to?
“⦣BDC” is simply a typo for “⦣BCD“
Perhaps designed to show Bob doesn’t really know all the angles.
Stop. Just stop.
Because the other side is equally long and you get to it through the equal angles?
what if the joke is not about angles but the initials cde = bdc. This is Canadian comic and these initials may be well known in Canada. I think cde stands for Canadian dollar equivalent. The bdc may be the French initials for a currency exchange.
I think we need a Canadian interpreter.
Stan, yes, that’s Freddie the Flying Fetus.
The third main character is Stumpy, a talking tree stump.
Yes, Freddy the Fetus is a regular character.
I can almost see the shape of a joke in the line “HA-HA!” given that one side is HA and they are all equal. But I just can’t quite find a joke there.
À votre service. The initialism bdc (in fashionable bold lowercase) serves as a logo for the Business Development Bank of Canada, a federal “Crown Corporation” that exists to lend money to entrepreneurs who are unable to obtain adequate financing elsewhere. It has, as far as I can see, no relevance to octagons, their sides, or angles.
Something to do with the octagon being in the shape of a stop sign? Which is something you’d normally see on roads — which you can then cross after you’ve stopped for the octagonal sign?
And possibly it’s got something to do with HA being one of the sides?
I mean, it’s still not funny, but it seems like that’s what we’re looking at here, right?