Diagonal communication is

Patterns of communication are called flows, and they are commonly classified according to the direction of interaction: downward, upward, horizontal, diagonal, and external.

🔑Key Points:
The term "diagonal communication" refers to multi-directional communication that includes horizontal, upward, and downward approaches.
It is Cross-functional communication between personnel at various levels of the organization.
Diagonal communication is a type of communication that combines vertical and horizontal elements. 
For example, when the vice president of sales sends an e-mail to the vice president of production inquiring when a product will be ready for shipping.
Building relationships between senior-level and lower-level personnel from various parts of the organization is one of the benefits.
Characteristics of diagonal communication that traverses all organizational units.
Staff members from several departments engage with one another in this manner, regardless of their reporting connection
Encourage a free flow of informal communication in the organization. 

🔴Additional Information:
Aggressiveness is a mode of communication and behavior where one expresses their feelings, needs, and rights without regard or respect for the needs, rights, and feelings of others.
The latent communication or the verbal communication is what we can trust because it is actually verbalized by speaking or reading. In that regard, it is very hard to misconstrue what has been said or what has been read. The other type of communication is referred to as meta-communication.