There are multiple times where ink is used as a stand-in for blood. Notable examples being the inklings exploding into splats of opposing ink when splatted, as well as Octarian bosses gushing out fountains of ink when their tentacles are destroyed.
When discussing Walleye Warehouse, sometimes you get this exchange;
Callie: Over in a quiet corner of the warehouse, two young Inklings are about to meet their destin- Marie:BATTLING! They're battling, aren't they?!
It's even more blatant in the European localization:
Callie: Off in a remote corner of the warehouse, two young Inklings are... Marie: BATTLING!
Some of the Splatfest announcements (particularly the American ones) can get a little suggestive. Marie referring to hot dogs as "cylinders of meat" might have been accidental, but there's nothing ambiguous about her response when Callie makes a reference to "plundering booty" while introducing Pirates vs. Ninjas.
Possibly unintentional, but Flow, the owner of the hat shop, in her introduction is considered by the squids to be their "crazy old aunt". While that in itself is innocent, it's pretty common to assign older people somebody has a close or caring relationship with as "aunt" or "uncle", that would still make her "aunt flow", a metaphor for a woman's menstrual cycle.
One of the chat logs in Octo Expansion has Pearl threatening that if anyone tries to harm Marina, she'll "cut a fish!"
Another chat log from Octo Expansion has Pearl mention a song she wrote before Off the Hook called "#$@%* Dudes Be #$@%* Sleepin'", which the stations refused to play "for obvious reasons". If you listen carefully to the demo's sound file in the log, you can hear a prolonged Sound-Effect Bleep.