When Shakespeare's sonnets were first published in 1609, they were assigned numbers instead of individual titles (Sonnets 1-154, to be exact). Sometimes they're referred to by their first lines, which is why Sonnet 29 is often called "When in disgrace with fortune and men's eyes."
So, rather than asking "What's up with the title?", we might instead ask "What's up with the first line?" After all, much like a title, this is the first thing that a reader will put their eyes on, and so it helps to set the tone and introduce the themes that will be developed as the poem unfolds.
In this case, we can focus on three key words and phrases: "disgrace," "fortune," and "men's eyes." To start with, "disgrace" introduces us both to the speaker's sad, sorry state, and to the idea of being out of heavenly favor, out of God's grace. Those two ideas will intertwine throughout the poem (check out our "Detailed Summary" for the deets). "Fortune," as well, is an idea that carries forward, in the form of a pun, as the speaker plays with the ideas of good luck and material wealth in that same word. Finally, "men's eyes" announces the issue of perception—both how the speaker sees himself, and how he sees the man he admires. The difference between those two viewpoints (in the speaker's eyes, anyway) is what accounts for the colossal bummer that he contemplates in the first part of the poem.
So, no title? No problem. This first line does everything that a good title would do for us, and then some.