So, first up: this trailer is red-band for a reason. Proceed with caution.
Right, then. For a few years in a child's life, any reference to poop or pee is inherently hilarious. The reference can be indirect. For years, I could make my kids laugh merely by intoning the word "underpants."
For many people (i.e., male people), these years commence somewhere around age five and conclude around the time when an even more dramatic biological phenomenon arises: the erection. It's not that scatological humor stops being funny, exactly. It's just that erections are so much more...urgent.
Given that, some credit is due, I suppose, to That Awkward Moment for managing to combine the twin dynamos of pelvic humor via a joke about being unable to urinate while enjoying the effects of Viagra. Unable, that is, unless you are horizontal. (See above.)
However. If three times is a trend, then the Enduring Erection is now officially a trailer trend, one that is bumping up hard against the peril of becoming a cliche. You all remember Love and Other Drugs, right? Right? At least that one could be forgiven for being about the introduction of Viagra to the market. Long-term side effects were a new thing.
But by the time Little Fockers makes a joke out of something, it's ready to be buried alongside Robert De Niro's reputation. Let it subside.