When I opened the door, the young fellow grinned sheepishly.
I/You/We/They have grinned. He/She/It has grinned.
The present perfect tense of "grin" is "have grinned."
I grinned at the person telling the joke.
The boy grinned at his mother because he had an idea.
Sentences can be constructed by using that word as an adjective or as a verb.
The People Who Grinned Themselves to Death was created in 1987-09.
yes
Grinned
of Grin
Sentences that are written using stress or accent are called exclamatory sentences. They usually are ended with an exclamation point.
Since you saw him grin when you did I am sure he knows he grinned at you.