Sandra and Woo involved this trope. When Ralph's pants get sliced off by Cloud, the last panel shows him in his heart boxers. In one of the comics, Woo literally tears off Sandra's clothes, including her shirt. All that's left on her is her underwear with hearts on them.
In the very first panel of Allen The Alien, Allen wears this type of boxers.
An early comic has Faye trying on a miniskirt before ultimately deciding not to buy it. The reason, as she explains to Martin, is that the skirt left her "one strong breeze away from letting the entire world know that I am wearing underpants with monkeys on them."
Seems to be a theme with Faye. A later comic had Martin putting a drunk Faye to bed and discovering she was wearing alligator-print undies.
In another Nerf NOW!! example, the RED Sniper is too distracted by Engie-Tan's strawberry panties to notice the BLU Pyro sneaking up behind him . . .