First Lover in the Nighttime? a little bit of bacon?

It seems to me that Shawn is joking about being Juliet's lover and the possibility of her cooking him bacon in the morning after they sleep together.

When he says "I'll get a title bump... something like First Lover in the Nighttime," he is saying (roughly) "If I help you get promoted, you'll declare me the best lover."

This is not the first time Shawn has used the phrase "lover in the nighttime." In the final episode of season 6, "Santabarbaratown", he jokes about him and Gus being "lovers in the nighttime... (like The Insiders except even more gay)".

When he says "Maybe a little bit of bacon," he is probably referring to the practice of a lover making breakfast for their partner who slept over.

The character Shawn often references bacon. I do not think this is a play on words related to the convention of calling law enforcement "pigs," as suggested by @Icy. Such a play on words would be inconsistent with the reference to being lovers who slept together.

A rough translation:

Shawn: (cont’d)… for us. Because you’ll be bumped up to Head Detective when Lassie gets promoted to Chief. Naturally, I’ll get a title bump as well. Something like, uh, First Lover in the Nighttime. Hmm? Maybe a little bit of bacon?

Shawn:... Because you [Juliet] will get a promotion. [...] When you do I will too. What will they call me? First Lover in the Nighttime? Or [alternately] your little bit of bacon? [a play on words - police have often been referred to as 'pigs']

In American English, the partners (usually spouses, as it is exceedingly rare in the US for such a high office holder to be unmarried) of heads of state are called "First Lady" or "First Gentleman". For example, First Lady of the United States is the title for the wife of the President of the United States. This designation may also be adopted by smaller political subdivisions, such as "First Lady of New York City", for the wife of the Mayor of New York City.

In the context of the show, since if Juliet chooses to stay in Santa Barbara, she will be promoted to Head Detective, Shawn jokes that he would like to be referred to as the First Lover in the Nighttime, as he has been shown to use the phrase "lover(s) in the night time" throughout the show to refer to significant others, and in this case the "First" implies he is the significant other to the highest-ranking police official (the running gag being "Lassie" doesn't count).

When someone in the US holds a public office (Mayor, Governor, President), their spouse is given the title "First (Gender)." So the president's wife is called "First Lady". Shawn is making a play on words, saying that if Juliet were to receive a promotion, he would be the "First Lover" essentially. And getting "a little bit of bacon" is getting more money.

The entire exchange is a phrase soup consisting of pseudo-jargon and confusing metaphors.

All references go to sex and money. The conversation appears to be happening while the couple are having sex. Hence, the "you are (my lover)".

"First Lover in the nighttime" is a coarse reference to the courtesy title normally awarded to spouses of higher government dignitaries.

Some users are suggesting that "bacon" is an indirect reference to policeman: that is totally believable. "Pig" (as a euphemism for police) has been re-appropriated by the very agencies that once found it a slur.

That said, in this case it is a double entendre: given the context, the meaning is more than obvious in its crude and sexual intent.

It is a reference to...

pork (verb) slang

to have sex with a person.

-The On-Line Slang dictionary

In this case it means... "to have sex with a policeman"

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On the other hand, we also have the saying to

bring home the bacon

to earn money for a family to live on:

Writers of these types of programs can spend hours discussing nuance after nuance, but conversation during intimate or emotional encounters does not usually achieve a level of "witty repartee".