Bola

The word bola can serve as a collective noun for groups of people.

• Una bola de mamilas = una bola de mamones = a bunch of pretentious, spoiled brats
• Una bola de víboras = a group of nasty, gossipy women
• Una bola de inútiles = a bunch of worthless, good-for-nothing, incompetent people
• Una bola de arrimados = a bunch of moochers, freeloaders
• Pinche bola de culeros, ¿no? What a bunch of assholes, don't you agree? (movie dialogue)

As you can see from these examples, bola depicts the group in question negatively.

En bola

Una actividad en bola is a group activity, one not performed alone. Vámonos en bola. Let's all go together, rather than separately. An email sent to a group would be un mail en bola.

Hacerse bolas

Hacerse bolas is an informal way to say get confused.

• Te vas a hacer bolas si escribes todo lo de las clases en el mismo cuaderno. You'll get really mixed up if you keep notes from all of your classes in the same notebook.
• Siempre me hago bolas. I can never remember how to do this. (Television character trying to open something complicated.)
• No te hagas bolas. Concentrate. Don't let yourself get confused.

The basic idea is that of making your head spin. Note that the verb is pronominal and the object is plural. The first time a new friend heard me use this expression, he commented on how surprising it was to hear from a foreigner. That's not always a welcome reaction, but it does underscore the informality of the expression.

Hacerle bolita

Hacerle bolita refers to a common prank where everybody chants ¡BO-LI-TA! ¡BO-LI-TA! while piling up on someone who is lying down or sleeping, forming a sort of ball (bolita) in the process.

Don't confuse this game with ¡Bolo, Bolo!, part of a baptism (bautizo) where the godfather (padrino) throws coins (el bolo) into the air for kids to scramble and gather them up.

Bolos are bowling pins. In Mexico the sport is called boliche.