Examples

Guònián de shíhou, wǒmen quán jiārén dōu jù zài yìqǐ, rè rè nào nào dì chī niányèfàn.
过年 的 时候 ,我们 全 家人 都 聚 在 一起 ,热 热 闹 闹 地 吃 年夜饭 。
At Chinese New Year, our whole family gathers together and joyously shares a New Year's Eve meal.

Tīnɡdào zhè ɡè xiāoxi, tā ɡāoɡāoxìnɡxìnɡ dì zǒu le.
听到 这 个 消息,她 高高兴兴 地 走 了。
Upon hearing the news, he happily left.

Wǒ qīnɡqīnɡchuchǔ dì kàndào tā ɡēn yī ɡè pànɡpànɡde nánrén shànɡ chē le.
我 清清楚楚 地 看到 他 跟 一 个 胖胖的 男人 上 车 了。
I clearly saw him get in the car with a fat man.

Using Reduplicated Adjectives as Predicates (ABAB)

If you use an adjective as a predicate, then you're basically using the adjective like a verb, and you reduplicate it as you would a verb, which means ABAB form. Using an adjective in this way is roughly equivalent to using 一下 after the (non-reduplicated) adjective.
Structure for ABAB
To use a reduplicated adjective as a predicate, follow this structure:
Subject + A B A B

In the pattern above there's no verb, because when an adjective serves as the predicate, it does the job of a verb. Notice also that there's no 的 after the ABAB, because it's not acting as an adjective.
Examples of ABAB

Jiéhūn de shíhou, rénmen xǐhuɑn rènɑo rènɑo.
结婚 的 时候 ,人们 喜欢 热闹 热闹。
People prefer to set off the fireworks to celebrate when they get married.

Mèimei kuài ɡuò shēnɡrì le, wǒ dǎsuɑn ɡěi tā bàn yī ɡè shēnɡrì pàiduì, rènɑo rènɑo.
妹妹 快 过 生日 了 ,我 打算 给 她 办 一 个 生日 派对 ,热闹 热闹 。
My little sister's birthday is coming and I'm going to celebrate it by throwing her a birthday party.

Lái, hē liǎnɡ bēi jiǔ, ɡāoxìnɡ ɡāoxìnɡ.
来,喝 两 杯 酒, 高兴 高兴。
C'mon, have a few glasses of wine and enjoy yourself.

Dào zhèlǐ lái, liánɡkuài liánɡkuài.
到 这里 来, 凉快 凉快。
Come over here and cool off.

Structure for AB 一下
The above structure is essentially equivalent to this one:
Subject + A B + 一下

Examples of AB 一下

Jiéhūn de shíhou, rénmen xǐhuɑn rènɑo yíxià.
结婚 的 时候 ,人们 喜欢 热闹 一下。
People prefer to set off the fireworks to celebrate when they get married.

Mèimei kuài ɡuò shēnɡrì le, wǒ dǎsuɑn ɡěi tā bàn yī ɡè shēnɡrì pàiduì, rènɑo yíxià.
妹妹 快 过 生日 了 ,我 打算 给 她 办 一 个 生日 派对 ,热闹 一下 。
My little sister's birthday is coming and I'm going to celebrate it by throwing her a birthday party.

Note: The "AABB" pattern for reduplication of two-syllable adjectives contrasts with the "ABAB" pattern for reduplication of two-syllable verbs.